Power Generation System Employing Power Amplifying Thermo-Mechanical Inverter Technology

ABSTRACT

Modern thermal power plants based on classical thermodynamic power cycles suffer from an upper bound efficiency restriction imposed by the Carnot principle. This disclosure teaches how to break away from the classical thermodynamics paradigm in configuring a thermal power plant so that its efficiency will not be restricted by the Carnot principle. The power generation system described herein makes a path for the next generation of low-to-moderate temperature thermal power plants to run at significantly higher efficiencies powered by renewable energy. This disclosure also reveals novel high-performance power schemes with integrated fuel cell technology, driven by a variety of fuels such as hydrogen, ammonia, syngas, methane and natural gas, leading toward low-to-zero emission power generation for the future.

CROSS-REFERENCE TO RELATED APPLICATIONS

This patent application is a continuation of U.S. Nonprovisional patentapplication Ser. No. 17/987,600, entitled “Power Generation SystemEmploying Power Amplifying Thermo-Mechanical Inverter Technology”, filedon Nov. 15, 2022; and U.S. application Ser. No. 17/987,600 claimspriority to U.S. Provisional Patent Application No. 63/424,374, entitled“Power Generation System Employing Power Amplifying Thermo-MechanicalInverter Technology”, filed on Nov. 10, 2022, and additionally claimspriority to U.S. Provisional Patent Application No. 63/279,662, entitled“Power Generation System Employing Power Amplifying Thermo-MechanicalInverter Technology”, filed on Nov. 15, 2021, all of the disclosures ofwhich are herein expressly incorporated by reference in theirentireties.

U.S. Nonprovisional patent application Ser. No. 17/987,600 also is acontinuation of International Patent Application Ser. No.PCT/US2022/049865, entitled “Power Generation System Employing PowerAmplifying Thermo-Mechanical Inverter Technology”, filed on Nov. 14,2022, the disclosure of which is hereby incorporated by reference as ifset forth in its entirety herein.

TECHNICAL FIELD

The devices and methods described here relates to a high-efficientthermal power plant powered by the low-to-medium grade heat (300-600°C.) and renewable energy technologies such as photovoltaic (PV) and/orhydrogen fuel cells. The system described herein also can be seen as athermo-mechanical inverter with a power-amplification which convertsDC-electric power generated in a renewable energy field to AC-electricpower that is fed to the main power-grid. The new inverter paradigmeliminates many issues related to conventional inertia-less electronicinverters, thus making the voltage and frequency control of the mainpower grid more economical.

BACKGROUND

Over the past century, humans have increased the concentration of CO₂ inthe atmosphere from 280 to more than 380 parts per million by volume,and it is growing faster every day. As the concentration of CO₂ hasrisen, so has the average temperature of the planet. Over the pastcentury, the average surface temperature of Earth has increased by about0.74° C. If CO₂ emissions continue to occur without restraint, thetemperatures are expected to rise by an additional 3.4° C. by the end ofthis century. Climate change of that magnitude would likely have seriousconsequences for life on Earth.

The electric power generation sector is the major source of the totalglobal CO₂ emissions, accounting for approximately 40% worldwide,followed by transportation, industry, and other sectors. The bottom lineis that thermal power plants that rely on fossil fuels like coal,natural gas, and other petroleum resources to generate electricityovershadow other sources in the electricity market. Thermal power plantsaccount for in excess of 80% of total power generation in mostcountries. For instance, thermal generating sources produce 82% of thetotal electricity in the United States, 84.3% in Australia, and 90% inemerging markets like India.

In spite of many technological advances in solar, wind, wave powergeneration, and hydrogen-related technologies, the principal hurdle toeliminate CO₂ emission is that thus far no equivalent (or better)technology has emerged, in terms of energy conversion efficiency, thanthe combustion-based thermal power plants, which run on fossil fuels forlarge-scale electric power generation. The main reason being that themodern thermal power plants based on the classical thermodynamic powercycles have an upper-bound restriction on the energy conversionefficiency imposed by the Carnot principle, which is determined by thehighest operating temperature of the cycle. In essence, to achieve highheat-to-power conversion efficiency, the cycle has to consume heat atthe highest possible temperature and burning fossil fuel makes it easierto achieve the required high temperatures, thereby enabling the powerplants to attain the required high thermal efficiencies.

Currently all the major large-scale power stations are facilitated bysteam turbine plants that run on Rankine cycle, gas power plants thatrun on Brayton cycle, solar photovoltaic (PV) power plants, wind turbineplants, and hydro power plants. Of these, steam turbine and gas turbinepower plants, which are extensively used throughout the world, needfossil fuels as the source of energy.

Among the leading renewable resources, solar PV technology has hadsubstantial growth in the past two decades, with the deployment rate ofsolar PV having an annual growth rate of 44% during 2000-2016. Similarto solar PV cells, which produce DC electricity, hydrogen fuel cellsalso can be identified as an alternative form of DC power generators.

In essence, to eliminate burning fossil fuels to generate electricity,the world is moving towards DC-electric power generation usingPV-arrays, hydrogen fuel cell technology, and wind-turbines. However,this new paradigm poses new problems. For example, flywheels of rotarygenerators store an immense amount of kinetic energy. When a largecontingency event occurs such as a large power generator goes off-line,the remaining online generators try to accommodate the imbalance betweensupply and demand due to the drop in generation by converting theirinertial kinetic energy into real power generation. This process, termedinertial response, slows the generators and results in a drop in gridfrequency. Inertial response provides time for the remaining onlinegenerators to detect changes in frequency and initiate their primaryfrequency response (PFR). As generator output from PFR increases, thenet imbalance reaches zero and the frequency decline stops. Eventually,the PFR schemes of online generators restore the power grid frequency tothe desired value.

Evidently, moving from conventional electro-magnetic-mechanical ACelectricity generators with large inertia to inertia-less DC electricitygenerators such as inverter-connected PV and hydrogen fuel celltechnologies reduces the system inertia, thus eliminating the inertialresponse, hence drastically impacting the power grid stability.

SUMMARY OF THE INVENTION

This disclosure describes a power generation system using PowerAmplifying Thermo-Mechanical Inverter (PATMI) technology, which is apower plant that converts DC electricity to AC electricity (see FIG. 1 )while amplifying the power output, thus delivering more power to thegrid than a conventional inverter does. However, the power amplificationrequires extra power to be fed to the device to keep in par with theprinciple of conservation of energy.

As FIG. 1 shows, the power amplification can be achieved by feeding thePATMI with low-grade thermal energy. Thus, the PATMI is essentially athermal power generation scheme. The studies carried out by the inventorshow that PATMI technology gives rise to a family of thermo-mechanicalpower schemes with considerably high efficiencies compared toconventional thermal power schemes, especially at low to mediumtemperature range (300-600° C.).

In accordance with one or more embodiments of the present invention,there is provided a power generation system that includes a firstsubsystem, the first subsystem including one or more mechanicalwork-consuming components, and the one or more mechanical work-consumingcomponents including at least one compressor or one pump; a secondsubsystem, the second subsystem including one or more components thatoutput mechanical work, and the one or more components that outputmechanical work including at least one expander; a third subsystem, thethird subsystem including one or more heat-consuming components, and theone or more heat-consuming components including at least one heatexchanger with an external thermal feed to the power generation system;and a fourth subsystem, the fourth subsystem including one or more heatsinks in the power generation system which dissipate heat to thesurroundings, the one or more heat sinks including a single heat sink orflue gas outlet. In these one or more embodiments, the first, second,third, and fourth subsystems are configured to interact with each otherby exchanging matter from one or more working fluids and by exchangingheat, such that the first, second, third, and fourth subsystemscooperate to maximize energy conversion efficiency. Also, in these oneor more embodiments, when the power generation system is in operationfor a particular finite time period, the first subsystem consumes W_(in)quantity of mechanical work from one or more external sources, the thirdsubsystem consumes Q quantity of heat from one or more external sources,while the second subsystem outputs W_(out) quantity of mechanical work,such that the energy conversion efficiency of the power generationsystem is given by: W_(out)/(W_(in)+Q).

The Essence and Merits of the Invention

A modern thermal power plant, despite its configurational complexity andsophistication, comprises of subsystems that fall into four basiccategories: (A) subsystems that consume mechanical power such ascompressors and/or fluid pumps; (B) subsystems that consume heat such asheating conduits, heat exchangers, heat regenerators, boilers,superheaters, and/or combustion chambers; (C) subsystems that delivermechanical power such as reciprocating or rotary (turbine) expanderswhich in turn drive conventional multi-phase AC electric powergenerators; and finally, (D) subsystems that dissipate heat to thesurroundings such as air-cooled and/or water-cooled heat exchangers andexhaust gas flues.

Assume a scenario where the power plant runs at steady state for a giventime period during which the subsystem (A) consumes a total of W_(in)mechanical energy and the subsystem (C) delivers a total of W_(out)mechanical energy to drive the AC-electric power generators, while thesubsystem (B) consumes a total of Q_(in) heat energy from external heatsources. Then in accordance with the conventional power plantconfiguration, since all power consuming devices (W_(in)) are driven bythe power produced by the power plant (W_(out)), the net power output ofthe power plant is W_(net)=(W_(out)−W_(in)), thus the efficiency of theconventional power plant is given by:

η_(conv)=(W _(out) −W _(in))/Q _(in)

However, if one takes an unconventional approach and decides to drivethe subsystem (A) completely independent of the rest of the power plantby providing W_(in) by any other external means, then this newconfiguration will have an efficiency given by:

η_(new) =W _(out)/(Q _(in) +W _(in))

Firstly, it can be shown by a simple algebraic manipulation thatη_(new)>η_(conv), as long as (W_(out)−W_(in))<Q_(in), which is assuredby the second law of thermodynamics. Secondly, one could assess themagnitude of the efficiency improvement Δη=η_(new)−η_(conv) and showthat it can be expressed as:

Δη=α[1−η_(con)] where α=[W _(in)/(Q _(in) +W _(in))]

Thus, it is evident that the efficiency improvement Δη is controlled bytwo factors. The first factor, a is the mechanical energy input as afraction of the total energy (heat and mechanical energy) input. Thesecond factor is [1−η_(con)] can be seen as room for improvement of theconventional efficiency to the perfect efficiency of unity. The equationfor Δη indicates that in order to get a significant efficiencyimprovement both factors need to be of considerable magnitudes.

For example, suppose, the modification is applied to a steam power plantor an ORC power plant, which runs on the Rankine power cycle, or a powerplant run on the Kalina cycle; in these cases W_(in) represents mainlythe pump work, which is highly insignificant in magnitude compared tothe heat input Q_(in), thus Δη improvement will not be of anysignificance due to the very low value of a. On the other hand, if themodification is applied to a gas turbine plant that runs on the Braytonpower cycle, assuming the maximum temperature of the cycle is around900˜1000° C., η_(conv) will be around 30˜35% and α will be in the range0.35˜0.5. In this case, the expected efficiency improvement Δη will be23˜35% (augmented), thus achieving a substantial efficiency improvementwhich falls in the range 53-70%.

Further, the PATMI technology can be adapted to the trendingsupercritical carbon dioxide (sCO₂) family of power plants. For example,in 2011, Sandia National Laboratories published¹ a design for a 100 MWesCO₂ cycle power plant driven by a nuclear reactor as the heat source.This plant, which is of the Split-Flow Recompression type (seeIllustrative Embodiment 9(b) for details), consists of two sets ofcompressors, a single turbine, and operates between the pressures 7 MPaand 20 MPa, with a peak operating temperature of 650° C. Themain-compressor and the re-compressor are designed to share the totalflow rate at 60%:40% ratio while consuming 10.1 MW and 21.0 MWrespectively, and the turbine outputs 131.1 MW mechanical power, whilethe heat consumption amounts to 200 MW. Thus, the power plant produces anet power output of 100 MWe at an efficiency of 50%. If one were toimplement the PATMI technology to this power plant, by driving thecompressors using (for example) hydrogen fuel cell technology, the poweroutput of the plant would be increased by ˜30%, and the efficiency willshow a moderate improvement of 6.7% (augmented). This marginalimprovement of the efficiency is not surprising as the controllingfactors of Δη, α and the (1−η_(conv)) are 0.135 and 50% respectively. 1.Mechanical Engineering magazine p. 60 No. 2, V. 143 February/March 2021;Sandia National Laboratories Report SAND 2011-2525, May

The power cycles which adopt the PATMI technology are fed with multipleforms of energy such as thermal energy and DC-electricity, the latter todrive the compressors. In such situations, how does one do anapples-to-apples comparison of the real efficiency gains. For thispurpose, let's define the tangible efficiency, meaning that theefficiency is expressed in terms of a single tangible fuel as if allenergy forms that fed to the power plant have been obtained from thissingle fuel. Consider the tangible fuel is hydrogen; the hydrogen burnsat 98% efficiency to provide heat for both cycles; and the hydrogen fuelcell efficiency is 60% for the PATMI cycle when the compressors aredriven by the DC-electricity generated by fuel cells.

In order to demonstrate the true merits of this invention, let us lookat the estimated but realistic performance of two versions of theBrayton-PATMI cycle power plants. The first Brayton version is aconventional Brayton cycle with an adiabatic turbine and multi-stagecompressors with intercooling. The second Brayton cycle version is anunconventional Brayton version with an isothermal turbine andmulti-stage compressors with intercooling. To distinguish the twoversions the latter version is called Brayton-isoTT-PATMI cycle (isoTTmeans iso-thermal-turbine).

The conventional Brayton example considered here is a 1 MWe Braytonpower plant comprised of three compression stages (with 0.8 isentropicefficiency) with intercooling, one turbine stage (with 0.9 isentropicefficiency), a heat input device (with hydrogen combustion efficiency of98%), and a regenerator (with 0.85 heat transfer effectiveness) with notemperature-imposed limits on regeneration.

FIG. 2 shows the estimated data in graphical form for a range of maximumtemperatures (300-900° C.) and for three distinct pressure ratios (PR=4,8, 12). On the left, the energy conversion efficiency of Brayton-PATMIcycle estimates are compared with the efficiencies of conventionalBrayton and the Carnot cycles; and on the right, the tangible efficiencyof Brayton-PATMI estimates are compared to the conventional Braytoncycle and Carnot efficiency.

As shown in the FIG. 2 , the Brayton-PATMI version shows a significantimprovement of the energy conversion efficiency over the conventionalBrayton cycle for the whole temperature range and for all pressureratios. Further, the efficiency of the PATMI version seems lesssensitive to temperature compared to the efficiency of the conventionalcycle. The most remarkable observation one can make is that the mostsignificant efficiency improvement seems to occur in the low to moderatetemperature range. The conclusion is that the PATMI technology enablesthe creation of highly efficient power plants that can operate at low tomoderate maximum cycle temperatures.

FIG. 3 shows a similar example for a 1 MWe Brayton-isoTT-PATMI powerplant. This power plant comprises of three compression stages (with 0.8isentropic efficiency with 0.9 effective intercoolers), onequasi-isothermal turbine stage (hydrogen is injected into the turbine),a heat input device to compensate the imperfect regeneration process(with hydrogen combustion efficiency of 98%), and a regenerator (with0.9 heat transfer effectiveness). The estimated data in graphical formis shown in FIG. 3 for a range of maximum temperatures (300-900° C.) andfor two pressure ratios (PR=4 and 8). On the left, the energy conversionefficiency of Brayton-isoTT-PATMI cycle estimates are compared with theefficiencies of Brayton-isoTT and the Carnot cycles; and on the right,the tangible efficiency of Brayton-isoTT-PATMI estimates are compared tothe Brayton-isoTT and Carnot cycle.

As FIG. 3 shows the Brayton-isoTT-PATMI seems to beat the Carnotefficiency restriction, especially at the lower temperature range (below400° C.). Similar to Brayton-PATMI power scheme, Brayton-isoTT-PATMIpower scheme also shows a remarkable efficiency improvement especiallyin the low-to-moderate temperature range (300-600° C.). Again, theconclusion is that the PATMI technology enables the power plants tooperate at low-to-medium temperatures and still perform at significantlyhigh efficiencies.

BRIEF DESCRIPTION OF THE FIGURES

The following diagrams are included in this disclosure:

FIG. 1 is a schematics representation of the PATMI technology.

FIG. 2 is a graph comparing the efficiencies of Brayton-PATMI and theconventional Brayton power schemes.

FIG. 3 is a graph comparing the efficiencies of Brayton-isoTT-PATMI andthe Brayton-isoTT power schemes

FIG. 4 is a schematic diagram of an Illustrative Embodiment of theinvention based on solar-PV-thermal driven Brayton-PATMI power scheme.

FIG. 5 is a schematic diagram of an Illustrative Embodiment of theinvention based on solar-PV-hydrogen driven Brayton-PATMI power scheme.

FIG. 6 is a schematic diagram of an Illustrative Embodiment of theinvention based on solar-PV-thermal-hydrogen driven Brayton-PATMI powerscheme with a bottoming cycle.

FIG. 7(a) is a schematic diagram of an Illustrative Embodiment of theinvention based on solar-PV-hydrogen driven Brayton-PATMI power schemewith sCO₂ bottoming cycle, which has a low-moderate temperature thermalfeed from the fuel cell

FIG. 7(b) is a schematic diagram of an Illustrative Embodiment of theinvention based on solar-PV-hydrogen driven Brayton-PATMI power schemewith sCO₂ bottoming cycle, which has a high temperature thermal feedfrom the fuel cell

FIG. 8 is a schematic diagram of an Illustrative Embodiment of theinvention based on the liquid-hydrogen driven Brayton-PATMI powerscheme.

FIG. 9 is a schematic diagram of an Illustrative Embodiment of theinvention based on solar-PV-hydrogen driven Brayton-isoTT-PATMI scheme.

FIG. 10 is a schematic diagram of an Illustrative Embodiment of theinvention based on hydrogen driven Brayton-Quasi-isoTT-PATMI (Config I)power scheme.

FIG. 11 is a schematic diagram of an Illustrative Embodiment of theinvention based on hydrogen driven Brayton-Quasi-isoTT-PATMI (Config II)power scheme.

FIG. 12(a) is a schematic diagram of an Illustrative Embodiment of theinvention based on sCO₂-PATMI basic regeneration scheme.

FIG. 12(b) is a schematic diagram of an Illustrative Embodiment of theinvention based on sCO₂-PATMI split-flow recompression scheme.

FIG. 12(c) is a schematic diagram of an Illustrative Embodiment of theinvention based on sCO₂-PATMI partial compression regeneration scheme.

FIG. 12(d) is a schematic diagram of an Illustrative Embodiment of theinvention based on sCO₂-PATMI partial cooling recompression scheme.

FIG. 12(e) is a schematic diagram of an Illustrative Embodiment of theinvention based on sCO₂-PATMI two-stage compression and two-stageheating scheme.

FIG. 12(f) is a schematic diagram of an Illustrative Embodiment of theinvention based on sCO₂-PATMI two parallel turbines (Config I) scheme.

FIG. 12(g) is a schematic diagram of an Illustrative Embodiment of theinvention based on sCO₂-PATMI two parallel turbines (Config II) scheme.

FIG. 13 is a schematic diagram of an Illustrative Embodiment of theinvention based on PATMI power generation scheme with a fuel cell drivencombined compressor/generator and a turbine driven generator.

FIG. 14 is a schematic diagram of an Illustrative Embodiment of theinvention based on two-stage PATMI power generation scheme with aby-pass cooling air stream and high-pressure gas turbine cycle.

FIG. 15 is a schematic diagram of an Illustrative Embodiment of theinvention based on two-stage PATMI power generation scheme with anauxiliary combustor in the by-pass air stream and high-pressure gasturbine cycle.

FIG. 16 is a schematic diagram of an Illustrative Embodiment of theinvention based on two-stage PATMI power generation scheme with twoauxiliary combustors and high-pressure gas turbine cycle feeding abottoming cycle.

FIG. 17 is a schematic diagram of an Illustrative Embodiment of theinvention based on two-stage PATMI power generation scheme where thelow-pressure turbine is fed with the combined exhaust from the fuel celland the high-pressure turbine.

FIG. 18 is a schematic diagram of an Illustrative Embodiment of theinvention based on two-stage PATMI power generation scheme with threeauxiliary combustors and a bottoming cycle driven by the high-pressuregas turbine cycle.

FIG. 19 is a schematic diagram of an Illustrative Embodiment of theinvention based on two-stage PATMI power generation scheme with afuel-feed, a steam-feed, a reformer, and fuel preheaters.

FIG. 20 is a schematic diagram of an Illustrative Embodiment of theinvention based on two-stage PATMI power generation scheme with areformer fed with steam generated using the exhaust of high-pressure gasturbine cycle.

FIG. 21 is a schematic diagram of an Illustrative Embodiment of theinvention based on two-stage PATMI power generation scheme with ahigh-pressure gas turbine cycle where turbine blades are cooled bysteam.

FIG. 22 is a schematic diagram of an Illustrative Embodiment of theinvention based on two-stage PATMI power generation scheme withpre-reformer/reformer and three regenerative heat exchangers in thehigh-pressure gas turbine cycle.

FIG. 23 is a schematic diagram of an Illustrative Embodiment of theinvention based on two-stage PATMI power generation scheme with aRankine bottoming cycle and a pre-reformer/reformer where bled-steamfrom Rankine turbine is used for fuel reformation.

FIG. 24 is a schematic diagram of an Illustrative Embodiment of theinvention based on two-stage PATMI power generation scheme with a fuelcell located downstream of the high-pressure gas turbine and steamrecirculation is assisted by an ejector.

FIG. 25 is a schematic diagram of an Illustrative Embodiment of theinvention based on two-stage PATMI power generation scheme with areformer and an advanced Rankine bottoming cycle having steam reheating.

FIG. 26 is a schematic diagram of an Illustrative Embodiment of theinvention based on three-stage PATMI power generation scheme withtwo-series Brayton/sCO₂ bottoming cycles.

DETAILED DESCRIPTION OF EMBODIMENTS

This disclosure describes a way in which the PATMI technology can beadopted to design superior power plants, whose performance is not behindered by the classical thermodynamic paradigm, eliminating therestrictions imposed by the Carnot principle on their energy conversionefficiencies.

The concepts introduced in this disclosure will apply to any thermalpower plant as long as it is comprised of the three major subsystems,namely the mechanical power consuming subsystem, the mechanical powerdelivering subsystem, and the heat consuming subsystem. Despite howthese three subsystems are connected to interact by exchanging matterand heat among them, as long as the mechanical power is not exchangedbetween the power consuming subsystem and the power deliveringsubsystem, the PATMI technology can be realized. Through the embodimentspresented in the following sections, this disclosure teaches how toadopt the PATMI technology to a number of conventional power cycles suchas Brayton, Brayton-isoTT, and sCO₂-schemes.

It should be pointed out that in the current state of the art ofheat-engine design, very little interest has been given to the Ericssoncycle as a viable power cycle as that the implementation of Ericssoncycle requires a design of an isothermal compressor and an isothermalexpander, which operate at the lowest and the highest temperatures ofthe cycle respectively. This means that every blade in the turbinerotors is exposed to the highest temperature of the cycle. As mentionedbefore, the current thermodynamics paradigm dictates that the highesttemperature of the cycle should be in the range 700-1200° C. to achievehigh thermal efficiencies, but no known metal as of today can withstandsuch high temperatures constantly and operate without structuralfailure. With the introduction of the PATMI technology, thisconventional norm is shattered. The PATMI technology enables the powercycles to operate at moderate temperatures (400-600° C.) whileperforming at superior efficiencies, thus making the isothermalexpanders and the superior regenerative Brayton-isoTT cycle a reality.Naturally, the configurations based on approximate-Ericsson(Brayton-isoTT) schemes show significantly better performance than theconfigurations based on the conventional Brayton cycle.

Illustrative Embodiment 1—Solar PV-Thermal Brayton-PATMI Power Scheme

This embodiment demonstrates how to reconfigure the basic Brayton cyclepower plant to perform in Solar PV-Thermal driven Brayton-PATMI scheme.Similar to a conventional Brayton cycle power plant, the power scheme asshown in FIG. 4 , comprises of a set of compression stages 2; a set ofturbine expansion stages 7; heat-input devices 5 a and 5 b to heat theworking fluid such as a set of heating conduits heated by concentratedsolar thermal units; and an optional heat regenerator 10. In theBrayton-PATMI configuration, the compression stages 2 are driven by arenewable energy source 50 such as solar-PV units and/or fuel cells,which are driven by solar-PV generated hydrogen. As a result, the totalpower generated by the turbine stages 7 is delivered to the ACelectricity generators 30, hence to the main power grid 60.

The workings of the solar PV-thermal driven Brayton-PATMI power schemecan be described as follows with reference to FIG. 4 . The DC-electricpower is generated in a renewable energy field 50 comprising of solar-PVcells, wind turbines, and/or any other renewable sources. So generatedDC-electric power is used to drive the DC-electric motors 40, which inturn drive the compression stages 2. The compressor stages 2 extractatmospheric air through the compressor inlet 1 which may be fitted witha filter or a strainer to remove particulate matter. The working fluidair that enters the compression stages 2 is compressed by the compressorstages, thereby increasing the pressure and the temperature of the air.In order to minimize the power consumption of the compression stages,air could be cooled at multiple stages between the compression stages(not shown in FIG. 4 ). The compression stages 2 deliver the compressedair at its maximum pressure through the compressor outlet line 3 to thelow-temperature flow passages 10 a of the optional regenerator 10.

The regenerator 10 is a heat exchanger device, which comprises oflow-temperature flow passages 10 a and high-temperature flow passages 10b running approximately in parallel, but in counter-flow directions,thereby facilitating highly effective heat transfer from thehigh-temperature fluid stream 10 b to the low-temperature fluid stream10 a that runs through the regenerator 10. The compressed air, whichenters the low-temperature flow passages 10 a of the regenerator throughthe compressor outlet 3 is heated by the high-temperature fluid streamthat flows in the high-temperature flow passages 10 b. Heated compressedair leaves the regenerator through the flowline 4 a.

The compressed air, now at its maximum pressure and at a certain hightemperature, flows into the working fluid heating device 5 a and 5 b,which are connected through the flowline 4 b. In this configuration, theworking fluid heating device is considered to be an externally heatedflow conduit-type, with a set of solar-thermal collectors as its heatsource. In order to achieve a maximum operating temperature in the range300-500° C., the solar collectors need to be of the concentrating-type.However, it could either be an imaging-type which tracks the sunthroughout the day, or a non-imaging type where sun-tracking is notessential. Another design variance that could arise here is the way inwhich the flow conduit of the power scheme working fluid and the solarthermal source are coupled. In the first variance, the solarconcentrator is designed so that concentrating mirrors directly heat theflow conduits by directing the reflected rays of the concentrator on tothe flow conduit. In the second variance design (not shown in the FIG. 4), the solar concentrator and the flow conduit are decoupled, and theheat is conveyed from the solar concentrator to the flow conduits by anintermediary phase-changing fluid such as water/steam using theheat-pipe principle.

The heated working fluid, now at its highest temperature enters theturbine stages 7 through the turbine feedline 6. The hot working fluidexpands passing through the turbine stages 7, while the turbine shaftoutputs the mechanical power harnessed by the turbine to the AC-electricgenerators 30. Eventually, the working fluid, now at a pressure somewhatclose to but above the atmospheric pressure, exits the turbine stages 7through the turbine outlet line 8 and enters the high-temperature flowpassages 10 b in the regenerator 10.

The hot working fluid, which enters the high-temperature flow passages10 b of the regenerator 10, rejects heat while heating up thelow-temperature working fluid stream, which flows in the low-temperatureflow passages 10 a of the regenerator. Cooled working fluid in thehigh-temperature flow passages 10 b, now at its lowest temperature,leaves the regenerator 10 through the exhaust line 9 and releases itselfto the atmosphere, thus completing the cycle.

Illustrative Embodiment 2—Solar-PV-Hydrogen-Powered Brayton-PATMI PowerScheme

The embodiment described here is another variance of the IllustrativeEmbodiment 1 described above, and the variation is due to how the powerscheme is powered. This Illustrative Embodiment is powered fully by thehydrogen gas generated in a renewable energy field, enabling thisembodiment to operate at a higher temperature range 500-900° C.

As shown in FIG. 5 the DC-electric power is generated in a renewableenergy field 50 comprising solar-PV cells, wind turbines, or any otherrenewable sources. In addition, the renewable energy field alsogenerates gaseous hydrogen by an electrolysis process 70, and thegenerated hydrogen gas is stored in gas storage unit 75. On occasionswhere the solar energy availability is low, the DC-electric power isalternatively generated by hydrogen fuel cell units 80 using a portionof the hydrogen gas in the gas storage 75. In scenarios where the fuelcell operating temperature is in the range 300-600° C., the waste heatrejected from the fuel cells can be used to augment the heat supply tothe Brayton cycle. This is achieved by the heat exchanger 80 a attachedto the fuel cell as shown in FIG. 5 .

The workings of this Brayton-PATMI power scheme can be described asfollows in reference to FIG. 5 . The power scheme comprises of a set ofcompression stages 2; a set of turbine expansion stages 7; a hydrogencombustion chamber 15 to internally heat the working fluid; and anoptional heat regenerator 10. In this hydrogen-driven Brayton-PATMIconfiguration, the compression stages 2 are driven by the electricmotors 40 which in turn are driven by the DC electricity generated usinghydrogen fuel-cell units 80. As a result, the total power generated bythe turbine stages 7 is delivered to the AC electricity generators 30,and subsequently to the main power grid 60.

The compression stages 2 extract atmospheric air through the compressorinlet 1, which may be fitted with a filter or a strainer to removeparticulate matter. The air that enters the compression stages 2 iscompressed while passing through the compressor stages, therebyincreasing the pressure and the temperature of the working fluid air. Inorder to minimize the power consumption of the compression stages 2, aircould be inter-cooled at multiple stages between the compression stages(FIG. 5 does not show this feature). The compression stages 2 deliverthe compressed air at its maximum pressure through the compressor outletline 3 to the low-temperature flow passages 10 a of the optionalregenerator 10.

The regenerator 10 is a heat exchanger device, which comprises oflow-temperature flow passages 10 a and high-temperature flow passages 10b running approximately in parallel, but in counter-flow directions,thereby facilitating highly effective heat transfer from thehigh-temperature fluid stream 10 b to the low-temperature fluid stream10 a. The compressed air which enters the low-temperature flow passages10 a of the regenerator 10 through the compressor outlet 3, is heated bythe high-temperature fluid stream which flows in the high-temperatureflow passages 10 b. Heated compressed air then exits the regeneratorthrough the flowline 4.

The compressed air, now at its maximum pressure and at a moderate hightemperature, flows into the fuel cell heat exchanger 80 a therebyheating the working fluid further. Heated compressed air flows throughthe combustion chamber feedline 5 and enters the combustion chamber 15.In the combustion chamber 15 the hydrogen gas is injected and ignited toheat the working fluid, enabling the working fluid to achieve itsmaximum operating temperature in the range 500-900° C.

The heated working fluid, now at its highest temperature, enters theturbine stages through the turbine feedline 6. The hot working fluidexpands, passing through the turbine stages 7, while the turbine shaftoutputs the mechanical power harnessed by the turbine. Eventually, theworking fluid, now at a pressure somewhat close to but above theatmospheric pressure, exits the turbine stages 7 through the turbineoutlet line 8 and enters the high-temperature flow passages 10 b in theregenerator 10.

The hot working fluid that flows in the high-temperature flow passages10 b of the regenerator 10 rejects heat while heating up thelow-temperature working fluid stream, which flows in the low-temperatureflow passages 10 a of the regenerator. The cooled working fluid in thehigh-temperature flow passages 10 b, now at its lowest temperatureleaves the regenerator 10 through the exhaust line 9 and releases itselfto the atmosphere, completing the cycle.

Illustrative Embodiment 3—Solar-PV-Thermal-Hydrogen Brayton-PATMI PowerScheme with a Bottoming Cycle Having a Thermal Feed from the PrimaryCycle

The embodiment described here is another variance of the IllustrativeEmbodiment 2 described above. The variation results from how the powerscheme is powered; as well as the incorporation of a bottoming-cycle togenerate extra power from the otherwise wasted heat. As shown in FIG. 6, this Illustrative Embodiment comprises of two power cycles; theprimary cycle is the Brayton-PATMI based power cycle, and the secondarycycle is a bottoming-cycle powered by a thermal feed from the primarycycle. The primary power cycle is powered by multiple heat sources,which also includes a hydrogen combustion chamber, enabling theconfiguration to operate at a higher temperature range (700-900° C.).Consequently, because the flue gas expelled from the primary cycleturbine is at a considerably high temperature, a secondarybottoming-cycle can be incorporated to harness extra power, increasingthe overall efficiency of the combined-cycle power scheme.

The secondary bottoming-cycle power unit could be any one of thelow-to-medium temperature (500-700° C.) power cycles such as the Rankinecycle, Organic Rankine cycle, Kalina cycle, and/or any form ofsupercritical power cycles. However, for this application, thesupercritical carbon dioxide (sCO₂) power cycles are preferred over theother cycles due to two reasons: (a) they have been proven to perform athigher efficiencies compared to other cycles (say 50% @ 650° C.); (b)their efficiencies can be further improved by incorporating the PATMItechnology described here. Details of the sCO₂-PATMI power schemes forbottoming-cycle applications are covered under the IllustrativeEmbodiments 9(a) though 9(g).

Similar to the Illustrative Embodiment 1 and 2, the DC-electric power isgenerated in a renewable energy field 50 comprising solar-PV cells, windturbines, and any other renewable sources. In addition, the renewableenergy field also generates gaseous hydrogen by an electrolysis process70, which is stored in a gas storage unit (not shown in FIG. 6 ). Onoccasions where the solar energy availability is low, the DC-electricpower is alternatively generated by the hydrogen fuel cell unit 80 usinga portion of the hydrogen gas in the gas storage. In scenarios where thefuel cell operating temperature is in the range 300-600° C., the wasteheat rejected from the fuel cells can be used to augment the heat supplyto the primary Brayton cycle. As shown in FIG. 6 , this is achieved bythe heat exchanger 80 a that is attached to the fuel cell.

The power scheme comprises of a set of compression stages 2 driven by aset of electric motors 40; a set of turbine expansion stages 11; fuelcell waste-heat exchanger 80 a; solar thermal collectors 7 a and 7 b; ahydrogen combustion chamber 15 to internally heat the working fluid; anoptional heat regenerator 10; and a high-temperature regenerative heatexchanger 20 to power a suitable bottoming cycle 90.

The workings of this Brayton-PATMI power scheme with a bottoming-cyclecan be described as follows in reference to FIG. 6 . The compressionstages 2 extract atmospheric air through the compressor inlet 1 whichmay be fitted with a filter or a strainer to remove particulate matter.The air that enters the compression stages 2 is compressed while passingthrough the compressor stages, thereby increasing the pressure and thetemperature of the working fluid air. In order to minimize the powerconsumption of the compression stages 2, air could be inter-cooled atmultiple stages between the compression stages (not shown in FIG. 6 ).The compression stages 2 deliver the compressed air at its maximumpressure through the compressor outlet line 3 to the waste-heatexchanger 80 a in the fuel cell unit 80, thus conveying the waste-heatof the fuel cell unit to the compressed air stream. The heated air thenflows through the feedline 4 to the low-temperature passages 10 a of theoptional regenerator 10.

One noteworthy aspect is that in this embodiment shown in FIG. 6 , theworking fluid flow sequence is set for compressed air to gain heat fromthe fuel cell waste-heat exchanger 80 a first and then from theregenerator 10. However, this flow sequence can be reversed if the fuelcell operation temperature is greater than the regenerator operatingtemperature, in which case the compressed air needs to flow in thelow-temperature passages 10 a of the regenerator 10 first and thenthrough the waste-heat exchanger 80 a of the fuel cell unit 80.

The regenerator 10 is a heat exchanger device, which comprises oflow-temperature flow passages 10 a and high-temperature flow passages 10b running approximately in parallel, but in counter-flow directions,thereby facilitating highly effective heat transfer from thehigh-temperature fluid stream 10 b to the low-temperature fluid stream10 a running through the regenerator 10. The compressed air which entersthe low-temperature flow passages 10 a of the regenerator 10 through theregenerator low-temperature feedline 4, is heated by thehigh-temperature fluid stream, which flows in the high-temperature flowpassages 10 b. The heated compressed air then exits the regeneratorthrough the flowline 5.

The compressed air, now at its maximum pressure and at a certain hightemperature, flows into the solar thermal collectors 7 a and 7 b insequence, which are connected through the flowline 6, thereby heatingthe compressed air further to a higher temperature. The heatedcompressed air enters the combustion chamber 15 through the combustionchamber feedline 8. In the combustion chamber 15, the hydrogen gas isinjected and ignited to heat the working fluid, thereby enabling theworking fluid to achieve its maximum operating temperature in the range700-900° C.

The heated working fluid, now at its highest temperature, enters theturbine stages 11 through the turbine feedline 9. The hot working fluidexpands, passing through the turbine stages 11, while the turbine shaftoutputs the mechanical power harnessed by the turbine to the AC-electricgenerators 30 which in turn supplies the generated electric power to themain power grid 60. Eventually, the expanded working fluid now at a lowpressure somewhat close to but above the atmospheric pressure, exits theturbine stages 11 through the turbine outlet line 12 and enters thehigh-temperature waste-heat exchanger 20.

The high-temperature regenerator 20 acts as a thermal feed to thebottoming-cycle 90. Thus, the bottoming-cycle working fluid passesthrough the low-temperature flow passages 20 a gaining heat, while theflue gas of the primary cycle cools down as it passes through thehigh-temperature flow passages 20 b rejecting much of itshigh-temperature heat to the bottoming cycle 90.

Eventually, the flue gas of the primary cycle leaves the waste-heatexchanger 20 through the flowline 13 and enters the regenerator 10. Theflue gas further rejects heat passing through the high-temperature flowpassages 10 b of the regenerator 10 and heats up the low-temperaturecompressed air, which flows in the low-temperature flow passages 10 a ofthe regenerator. The cooled flue gas, now at its lowest temperature,leaves the high-temperature flow passages 10 b of the regenerator 10through the exhaust line 14 and releases itself to the atmosphere, thuscompleting the primary cycle.

This Illustrative Embodiment describes the use of a secondarybottoming-cycle driven by a thermal feed from an open-air primary cyclepower scheme, thus achieving a higher overall efficiency of thecombined-cycle power scheme. In a similar manner a closed-cycle powerscheme could be used as the primary cycle to drive a suitable bottomingcycle. Such an Illustrative Embodiment will be discussed in a latersection.

Illustrative Embodiment 4—Solar-PV-Hydrogen Brayton-PATMI Power Schemewith a sCO₂ Bottoming Cycle Thermal Feed is Augmented with the Fuel CellWaste Heat

The embodiments described here are variances of the IllustrativeEmbodiment 3 described above and the variances result from how thebottoming-cycle thermal feed is arranged. In the Illustrative Embodiment3 the bottoming-cycle thermal feed solely came from the primary cyclewhile the waste-heat from the fuel cell was fed to the primary cycle.However, in these variances the bottoming-cycle is fed with the thermalfeed from the primary cycle as well as from the fuel cell waste-heatfeed. As a result, depending on the fuel cell operating temperaturerange is higher (or lower) with respect to the temperature of theprimary cycle thermal feed to the bottoming cycle, two thermal feedconfigurations result for the bottoming-cycle. These two variances aredescribed in the following sections under the Illustrative Embodiment4(a) and the Illustrative Embodiment 4(b).

Illustrative Embodiment 4(a)—the sCO₂ Bottoming Cycle Gets HigherTemperature Heat from the Primary Cycle Thermal Feed

As shown in FIG. 7(a), this Illustrative Embodiment comprises of twopower cycles: the first is the Brayton-PATMI primary gas power cycle;and the second is the secondary bottoming-cycle power unit. The primarypower cycle is powered by multiple heat sources which also include ahydrogen combustion chamber, thus enabling this configuration to operateat a higher temperature range (700-900° C.). Consequently, the flue gasexpelled from the primary cycle turbine is at a considerably hightemperature, a secondary bottoming-cycle can be incorporated to harnessextra power, thus augmenting the overall efficiency of thecombined-cycle power scheme. The secondary bottoming-cycle power unitcould be any one of the low-to-medium temperature (500-700° C.) powercycles; however, for this application the supercritical carbon dioxide(sCO₂) power cycles are preferred due to the reasons mentioned inreference to the Illustrative Embodiment 3.

Similar to the Illustrative Embodiment 3, the DC-electric power isgenerated in a renewable energy field 50 comprising solar-PV cells, windturbines, and any other renewable sources. In addition, the renewableenergy field also generates gaseous hydrogen by an electrolysis process70, and so generated hydrogen gas is stored in gas storage unit 75. Onoccasions where the solar energy availability is low, the DC-electricpower is alternatively generated by the hydrogen fuel cell unit 80 usinga portion of the hydrogen gas in the gas storage.

The power scheme comprises of a set of compression stages 2 driven by aset of electric motors 40; a set of turbine expansion stages 7; ahydrogen combustion chamber 15 to internally heat the working fluid; anoptional low-temperature heat regenerator 10; fuel cell waste-heatexchanger HX₁; and a high-temperature regenerative heat exchanger HX₂ tothermally power the sCO₂ bottoming cycle 90. For this IllustrativeEmbodiment it is assumed that the primary cycle thermal feed to thebottoming-cycle has a higher temperature than the temperature of thefuel cell waste-heat feed.

The workings of this Brayton-PATMI power scheme with a bottoming-cyclecan be described as follows with reference to FIG. 7(a). The compressionstages 2 extract atmospheric air through the compressor inlet 1 whichmay be fitted with a filter or a strainer to remove particulate matter.The air that enters the compression stages 2 is compressed while passingthrough the compressor stages, thereby increasing the pressure and thetemperature of the working fluid air. In order to minimize the powerconsumption of the compression stages 2, air could be inter-cooled atmultiple stages between the compression stages (FIG. 7(a) does not showthis feature). The compression stages 2 deliver the compressed air whichis at its maximum pressure, to the optional low-temperature regenerator10 through the compressor outlet line 3.

The regenerator 10 is a heat exchanger device which comprises oflow-temperature flow passages 10 a and high-temperature flow passages 10b running approximately in parallel, but in counter-flow directions,thereby facilitating highly effective heat transfer from thehigh-temperature fluid stream 10 b to the low-temperature fluid stream10 a. The compressed air, which enters the low-temperature flow passages10 a through the regenerator low-temperature feedline 3 is heated by thehigh-temperature fluid stream, which flows in the high-temperature flowpassages 10 b. The heated compressed air then exits the regeneratorthrough the flowline 4.

The compressed air, now at a certain high temperature, enters thecombustion chamber 15 through the feedline 4. In the combustion chamber15 the hydrogen gas is injected and ignited to heat the working fluid,thereby enabling the working fluid to achieve its maximum operatingtemperature in the range 700-900° C. As a variance to this IllustrativeEmbodiment, solar thermal heating option (not shown in FIG. 7(a)) can beincluded as a secondary thermal feed to the primary cycle. So heatedworking fluid, now at its highest temperature, enters the turbine stages7 through the turbine feedline 6. The hot working fluid expands passingthrough the turbine stages 7 while the turbine shaft outputs themechanical power harnessed by the turbine to the AC-electric generators30 which in turn supplies the generated AC-electric power to the mainpower grid 60. Eventually, the expanded working fluid, now at a lowpressure somewhat close to but above the atmospheric pressure, exits theturbine stages 7 through the turbine outlet line 8 and enters thehigh-temperature waste-heat exchanger HX₂.

Eventually, the flue gas of the primary cycle leaves the waste-heatexchanger HX₂ through the flowline 9 and enters the low-temperatureregenerator 10. The flue gas further rejects heat passing through thehigh-temperature flow passages 10 b of the regenerator 10 and heats upthe low-temperature compressed air, which flows in the low-temperatureflow passages 10 a of the regenerator. The flue gas, having rejectedheat in the flow passages 10 b, leaves the high-temperature flowpassages 10 b of the regenerator 10 through the exhaust line 11, thuscompleting the primary cycle.

The high-temperature regenerator HX₂ acts as one of the thermal feeds tothe bottoming-cycle 90, whereas the waste-heat exchanger HX₁ of the fuelcell acts as the second thermal feed to the bottoming-cycle. For thisIllustrative Embodiment it is assumed that the fuel cell waste-heat feedis at a lower temperature range (400-500° C.) compared to thetemperature of the exhaust flue gas expelling from the primary cycleturbine 7. Therefore, the bottoming-cycle working fluid carbon dioxidegains heat by passing through the waste-heat exchanger of the fuel cellHX₁ first and then gains further heat from the low-temperature flowpassages of HX₂. Accordingly, the bottoming-cycle working fluid flowsfrom the feedline 12 a to the heat exchanger HX₁ first; then the workingfluid is conveyed to the HX₂ through the feedline 12 b; and finally, theworking fluid flows through the feedline 12 c to complete thebottoming-cycle.

The bottoming-cycle compressors are driven by the electric motors 40 awhich in turn are driven by the renewable energy field 50, while thegenerators 30 a coupled to the turbine expanders of the bottoming-cyclegenerate AC-electric power to augment the power output to the main powergrid 60.

One noteworthy consequence of this arrangement is that since the exhaustflue gas temperature of the primary cycle turbine determines the highesttemperature of the sCO₂ bottoming-cycle, to obtain high overallperformance the primary cycle pressure ratio needs to be in a moderaterange.

Illustrative Embodiment 4(b)—the sCO₂ Bottoming Cycle Gets HigherTemperature Heat from the Fuel Cell Waste Heat Feed

This embodiment, to a very high degree, is similar to the IllustrativeEmbodiment 4(a) described in the previous section, however with a subtlevariance based on how the thermal feeds of the bottoming-cycle arearranged. As shown in FIG. 7(b), this Illustrative Embodiment comprisesof two power cycles: the first is the Brayton-PATMI primary gas powercycle; and the second is the secondary bottoming-cycle power unit. Theprimary power cycle is powered by multiple heat sources which alsoinclude a hydrogen combustion chamber, thus enabling this configurationto operate at a higher temperature range (700-900° C.). Consequently,the flue gas expelled from the primary cycle turbine is at aconsiderably high temperature, a secondary bottoming-cycle can beincorporated to harness extra power, thus augmenting the overallefficiency of the combined-cycle power scheme. The secondarybottoming-cycle power unit could be any one of the low-to-mediumtemperature (500-700° C.) power cycles, however, for this applicationthe supercritical carbon dioxide (sCO₂) power cycles are preferred dueto the reasons mentioned in reference to the Illustrative Embodiment 3.

Similar to the Illustrative Embodiment 4(a), the DC-electric power isgenerated in a renewable energy field 50 comprising solar-PV cells, windturbines, and any other renewable sources. In addition, the renewableenergy field also generates gaseous hydrogen by an electrolysis process70, and so generated hydrogen gas is stored in gas storage unit 75. Onoccasions where the solar energy availability is low, the DC-electricpower is alternatively generated by the hydrogen fuel cell unit 80 usinga portion of the hydrogen gas in the gas storage.

The power scheme comprises of a set of compression stages 2 driven by aset of electric motors 40; a set of turbine expansion stages 7; ahydrogen combustion chamber 15 to internally heat the working fluid; anoptional low-temperature heat regenerator 10; a high-temperatureregenerative heat exchanger HX₁; and a fuel cell waste-heat exchangerHX₂ to thermally power the sCO₂ bottoming cycle 90.

The major variance between the Illustrative Embodiments 4(a) and 4(b) isbased on which of the two thermal feeds to the sCO₂ bottoming-cycle isthe high temperature feed. For the Illustrative Embodiment 4(a) it wasassumed that the primary cycle thermal feed is at a higher temperaturecompared to the temperature of the fuel cell thermal feed. In thisIllustrative Embodiment it is assumed that the fuel cell thermal feed isat a higher temperature; for example, the fuel cell could be of amolten-carbonate type which operates at the temperature range (600-700°C.). Under these conditions the flue gas expelled from the primary cycleturbine can provide the low-temperature thermal feed to the sCO₂bottoming-cycle. One advantage of this scenario is that the pressureratio of the primary cycle need not be restricted to the moderate range,meaning that the primary cycle can generate more power compared to theIllustrative Embodiment 4(a).

The workings of this Brayton-PATMI power scheme with the sCO₂bottoming-cycle can be described as follows with reference to FIG. 7(b).The compression stages 2 extract atmospheric air through the compressorinlet 1 which may be fitted with a filter or a strainer to removeparticulate matter. The air that enters the compression stages 2 iscompressed while passing through the compressor stages, therebyincreasing the pressure and the temperature of the working fluid air. Inorder to minimize the power consumption of the compression stages 2, aircould be inter-cooled at multiple stages between the compression stages(FIG. 7(b) does not show this feature). The compression stages 2 deliverthe compressed air which is at its maximum pressure, to the optionallow-temperature regenerator 10 through the compressor outlet line 3.

The regenerator 10 is a heat exchanger device, which comprises oflow-temperature flow passages 10 a and high-temperature flow passages 10b running approximately in parallel, but in counter-flow directions,thereby facilitating highly effective heat transfer from thehigh-temperature fluid stream 10 b to the low-temperature fluid stream10 a. The compressed air, which enters the low-temperature flow passages10 a of the regenerator 10 through the regenerator low-temperaturefeedline 3, is heated by the high-temperature fluid stream which flowsin the high-temperature flow passages 10 b. The heated compressed airthen exits the regenerator through the flowline 4.

The compressed air, now at a certain high temperature, enters thecombustion chamber 15 through the feedline 4. In the combustion chamber15 the hydrogen gas is injected and ignited to heat the working fluid,thereby enabling the working fluid to achieve its maximum operatingtemperature in the range 700-900° C. As a variance to this IllustrativeEmbodiment, solar thermal heating option (not shown in FIG. 7(b)) can beincluded as a secondary thermal feed to the primary cycle. So heatedworking fluid, now at its highest temperature, enters the turbine stages7 through the turbine feedline 6. The hot working fluid expands passingthrough the turbine stages 7 while the turbine shaft outputs themechanical power harnessed by the turbine to the AC-electric generators30 which in turn supplies the generated AC-electric power to the mainpower grid 60. Eventually, the expanded working fluid, now at a lowpressure somewhat close to but above the atmospheric pressure, exits theturbine stages 7 through the turbine outlet line 8 and enters thehigh-temperature waste-heat exchanger HX₁.

Eventually, the flue gas of the primary cycle leaves the waste-heatexchanger HX₁ through the flowline 9 and enters the low-temperatureregenerator 10. The flue gas further rejects heat passing through thehigh-temperature flow passages 10 b of the regenerator 10 and conveysheat to the compressed air, which flows in the low-temperature flowpassages 10 a of the regenerator. The flue gas, having rejected heat inthe flow passages 10 b, leaves the flow passages 10 b of the regenerator10 through the exhaust line 11, thus completing the primary cycle.

The primary cycle thermal feed through the heat exchanger HX₁ acts asthe low-temperature thermal feed to the bottoming-cycle 90, whereas thewaste-heat exchanger HX₂ of the fuel cell acts as the high-temperaturethermal feed to the bottoming-cycle. For this Illustrative Embodiment itis assumed that the fuel cell waste-heat feed is at a high temperaturerange (600-700° C.) compared to the temperature of the exhaust flue gasexpelling from the primary cycle turbine 7. Therefore, thebottoming-cycle working fluid, carbon dioxide gains heat by passingthrough the low-temperature primary cycle thermal feed HX₁ first andthen gains further heat from the high-temperature fuel cell waste-heatexchanger HX₂. Accordingly, the bottoming-cycle working fluid flows fromthe feedline 12 a to the heat exchanger HX₁ first; then the workingfluid is conveyed to the HX₂ through the feedline 12 b; and finally, theworking fluid flows through the feedline 12 c to complete thebottoming-cycle.

The bottoming-cycle compressors are driven by the electric motors 40 a,which in turn are driven by the renewable energy field 50, while thegenerators 30 a coupled to the turbine expanders of the bottoming-cyclegenerate AC-electric power to augment the power output to the main powergrid 60.

Illustrative Embodiment 5—Liquid Hydrogen Driven Brayton-PATMI PowerScheme

In the Illustrative Embodiments 2, 3, and 4 the hydrogen gas to drivethe power scheme is assumed available in the gaseous form. Suppose,hydrogen is transported for greater distances in the liquid form, amajor portion of the energy consumed in liquefying the hydrogen gas canbe recovered by using liquid hydrogen in pre-coolers, intercoolers, andpost-coolers placed before, in between, and after the compressionstages. In doing so, not only a major portion of the energy consumptionof the compression stages is saved, but also the hydrogen is heated andbrought to the gaseous state. The Illustrative Embodiment 5 describedhere is a variance of the Illustrative Embodiment 2 with theincorporation of liquid hydrogen as the fuel source.

Similar to the Illustrative Embodiments 2, 3, and 4 this IllustrativeEmbodiment as shown in FIG. 8 , comprises of a set of compression stages3, 6, 9, and 12; a set of turbine expansion stages 17; a hydrogencombustion chamber 15 to internally heat the working fluid; an optionalheat regenerator 10 to regenerate heat which otherwise would have beenwasted; and a hydrogen fuel cell system 80 to provide electrical powerto drive the compression stages by a set of DC-electric motors 40. Inaddition, this Illustrative Embodiment contains a series of heatexchanger devices IC₁ through IC₃ and PrC to cool the working fluid airwith very cold liquid hydrogen. While these heat exchanger devices areused in the compression process, one post-cooler PoC is used to cool theflue gas emitting from the power scheme. Apart from the main cycle flowscheme, a second flow scheme carries the liquid hydrogen which exists at(approx.) −240° C.

The workings of the liquid hydrogen driven Brayton-PATMI power schemecan be described as follows in reference to FIG. 8 , which depicts thepower scheme comprising of four compression stages 3, 6, 9, 12 as anexample. The first compression stage 3 (comp₁) extracts atmospheric airthrough the plant's air inlet 1 which may be fitted with a filter or astrainer to remove particulate matter. The air that flows through thefeedline 1 enters the first precooler PrC, which cools the air at theatmospheric conditions to a very low temperature (approx. −130° C.) bythe liquid-hydrogen. The cold air in the precooler PrC is then extractedthrough the feedline 2 to the first compression stage 3 (comp₁). Theair, which enters the compressor is compressed to a certain degree inthe first compression stage 3, and is delivered to the first intercoolerIC₁ through the feedline 4. This sequence of progressive compression andintercooling of air occurs in the next two compression stages 6 (comp₂)and 9 (comp₃) followed by the intercoolers IC₂ and IC₃. In these twostages the air is extracted to the compression stages through theirindividual inlet lines 5 and 8, while the air is delivered to theintercoolers through their individual outlet lines 7 and 10. The lastcompression stage 12 (comp₄) extracts air, which is already compressedto a very high degree through the feedline 11, and compresses air to thehighest pressure of the cycle. The compressed air is then delivered tothe optional regenerator 10 through the feedline 13. At this point thecompressed air temperature is expected to be around −100° C.

The regenerator 10 is a heat exchanger device, which comprises oflow-temperature flow passages 10 a and high-temperature flow passages 10b running approximately in parallel, but in counter-flow directions,thereby facilitates highly effective heat transfer from thehigh-temperature fluid stream 10 b to the low-temperature fluid stream10 a. The compressed air, which enters the low-temperature flow passages10 a through the compressor outlet 13 is heated by the high-temperaturefluid stream, which flows in the high-temperature flow passages 10 b.The heated compressed air then exits the regenerator (temperature in therange 400-450° C.) through the flowline 14.

The compressed air, now at its maximum pressure and at a certain hightemperature, flows into the combustion chamber 15, where the hydrogengas is injected and ignited to heat the working fluid. This enables theworking fluid to achieve its maximum operating temperature in the range700-800° C. The heated working fluid, now at its highest temperature,enters the turbine stages 17 through the turbine feedline 16. The hotworking fluid expands through the turbine stages 17 while the turbineshaft 30 delivers the mechanical power output harnessed in the turbineto the AC-generators (not shown in FIG. 8 ). Eventually, the workingfluid, now hot flue gas at a pressure somewhat close to but above theatmospheric pressure, exits the turbine stages 17 through the turbineoutlet line 18 and enters the high-temperature flow passages 10 b in theregenerator 10.

The hot working fluid, which enters the high-temperature flow passages10 b of the regenerator 10, rejects heat while heating up thelow-temperature working fluid stream 10 a. The cooled flue gas streamnow at a certain low temperature leaves the regenerator 10 through theexhaust line 19. Eventually, the flue gas passes through the post-coolerPoC, thereby heating the low-temperature hydrogen to its gaseous state.In this post-cooling process, water vapor in the flue gas condenses andultimately releases itself to the atmosphere through the exhaust line21, completing the cycle of the working fluid air.

In this Illustrative Embodiment, the liquid hydrogen undergoes a seriesof processes described as follows. Liquid hydrogen is pumped into thepower plant by the pump 50 to the pre-cooler PrC through its feedline51. Subsequently, the liquid hydrogen flows through the intercoolersIC₁, IC₂, IC₃ fed by their feed lines 52, 53, 54, thereby cooling theworking fluid air in between the compression stages 3, 6, 9, 12.Eventually, the liquid hydrogen passes through the feedline 55 andenters the post-cooler PoC to cool the flue gas which enters through theexhaust line 19. The post-cooler PoC converts all the liquid hydrogen togaseous hydrogen, and the generated hydrogen gas enters the storage tank75 through the feedline 56. The hydrogen gas which is stored in thestorage tank 75, is fed to the combustion chamber 15 through a meteringdevice (not shown in FIG. 8 ) located in the fuel feedline 59. In asimilar manner, the hydrogen gas is metered through the fuel feedline 58to the fuel cell system 80 which provides DC-electric power to drive thecompressor stages.

A number of variances of the Illustrative Embodiment described above canbe devised by allowing the heat liberated by the fuel cell to be usedsuitably to heat up the compressed air in the main power cycle, whichsaves some hydrogen fuel used in the combustion chamber. However, thelocation at which this heat injection occurs depends on whether the fuelcell operates at a low, moderate, or high temperature. If the fuel celloperates at a high temperature (above 500° C.), then the heat rejectedby the fuel cell can be used to heat up the compressed air by placingthe fuel cell waste-heat exchanger in the flowline 14. On a similarrationale, if the fuel cell operating temperature is moderate to low(below 500° C.), a similar heat exchanger can be placed in the flowline13. On the other hand, the waste heat liberated by the fuel cell canalso be used to heat up the hydrogen fuel in the fuel feedlines 58 or 59and/or on the liquid hydrogen feedlines 55 or 56.

Illustrative Embodiment 6—Solar-PV-Hydrogen Driven Brayton-isoTT-PATMIPower Scheme

Under the section titled The Essence and Merits of the Invention, it wasshown that adopting the PATMI technology to a power unit, which runs onthe Brayton-isoTT cycle increases its efficiency beyond the Carnotefficiency. This disclosure demonstrates how to reconfigure aBrayton-isoTT cycle power plant to perform in Brayton-isoTT-PATMI schemepowered by the hydrogen gas. The Brayton cycle and the Brayton-isoTTcycle, to a greater degree, are very similar, except in the way thatheat is provided to the cycles. In the Brayton cycle, the working fluidis heated in an isobaric process prior to the expansion process, thelatter being an adiabatic process. In order to minimize the compressionwork in the Brayton cycle, the heat is removed in between thecompression stages by incorporating inter-coolers. The regenerator isoptional in the Brayton cycle. Although the cycle can operate without aregenerator, having a regenerator increases the energy conversionefficiency.

In the Brayton-isoTT cycle described here consists of inter-cooledmulti-stage compression process and multiple fuel injection points inthe turbine between expansion stages, coupled with a high-performingregenerator with 90-95% heat transfer effectiveness.

As shown in FIG. 9 , this Illustrative Embodiment comprises of a set ofcompression stages 2 a, 2 b, 2 c, 2 d; a set of turbine expansion stages5; and a heat regenerator with a high heat transfer effectiveness 10. Inthis Brayton-isoTT-PATMI configuration, the compression stages aredriven by a set of DC-electric motors 40 which are in turn powered bythe DC-electricity generated in a renewable energy field 50 or using ahydrogen fuel-cell 80. As a result, the total power generated by theturbine stages is fully delivered to the AC-electric generators 30,which in turn supplies power to the main power grid 60.

The workings of this Brayton-isoTT-PATMI power scheme can be describedas follows in reference to FIG. 9 . A renewable field 50 containsDC-electric power generators such as solar PV-arrays, wind generators,and electric energy storage devices such as batteries, so that generatedDC-electricity can be stored in the batteries. A portion of this storedenergy is used to generate hydrogen gas in an electrolysis operation 70and so generated hydrogen is stored in a hydrogen storage tank 75. Whenthe renewable energy availability is scarce, a set of hydrogen fuelcells 80 uses a portion of the stored hydrogen to generateDC-electricity which augment the stored electric energy in batteries.The generated DC-electric power drives the compression stages 2 athrough 2 d, enabling the extraction of the atmospheric air through thecompressor inlet 1, which may be fitted with a filter or a strainer toremove particulate matter. The air that enters the compression stage 2 ais compressed to a certain pressure while the temperature of the air isalso increased to a certain degree. The partially compressed air thenflows through the intercooler IC₁. In the intercooler the air is cooledto a lower temperature while the pressure more or less remains the same.The cooled air now at a certain higher pressure enters the nextcompressor stage 2 b where the air is compressed further. As FIG. 9shows, this alternate compression and intercooling continue through thecompressor stages 2 b, 2 c, and 2 d and the intercoolers IC₂ and IC₃,thereby compressing the air to the highest pressure of the cycle whileits temperature increase is kept to a minimum. The compressed workingfluid air, now at a mildly higher temperature is delivered through thecompressor outlet line 3 to the low-temperature flow passages 10 a ofthe regenerator 10.

As was the case with the previously described Illustrative Embodiments,the regenerator 10 is a heat exchanger device, which comprises oflow-temperature flow passages 10 a and high-temperature flow passages 10b running approximately in parallel, but in counter-flow directions,facilitates highly effective heat transfer (effectiveness 90-95%) fromthe high-temperature fluid stream 10 b to the low-temperature fluidstream 10 a. The compressed air, which flows through the low-temperatureflow passages 10 a of the regenerator 10, is heated by thehigh-temperature fluid stream which flows in the high-temperature flowpassages 10 b. The heated compressed air exits the regenerator throughthe turbine feedline 4.

The working fluid, now heated to (or very close to) the highesttemperature of the cycle, enters the turbine stages 5. The hot workingfluid expands through the turbine stages 5 while the hydrogen fuel isinjected and ignited into the turbine at multiple points locatedstrategically between the expansion stages to maintain the temperatureof the expanding gas at its maximum value of the cycle. The workingfluid expansion process enables the turbine 5 to output the mechanicalpower harnessed in the turbine to the AC-electric generator 30. Theexpansion process in the turbine 5 continues until the air (now containsa minute quantity of water vapor) reaches a pressure close to but abovethe atmospheric pressure while its temperature reaches a value somewhathigher than the compressed air temperature at the turbine inlet.Eventually, the working fluid containing a minute quantity of watervapor exits the turbine stages 5 through the turbine outlet line 6 andenters the high-temperature flow passages 10 b in the regenerator 10.

The hot working fluid flows through the high-temperature flow passages10 b of the regenerator 10 and rejects heat while heating up thelow-temperature working fluid stream, which flows in the low-temperatureflow passages 10 a of the regenerator. The cooled working fluid in thehigh-temperature flow passages 10 b, now at its lowest temperature,leaves the regenerator 10 through the exhaust line 7 and releases itselfto the atmosphere, completing the cycle.

It is worth highlighting that in order to begin the quasi-isothermalexpansion process in the turbine at the highest temperature of thecycle, the hot compressed air needs to be at the highest temperature ofthe cycle at the inlet of the turbine (flowline 4). However, due to theimperfect regenerative process in the regenerator 10 the temperature ofthe heated compressed air leaving the regenerator through the flowline 4will always be lower than the temperature of the hot gas that enters theregenerator through the flowline 6. This can be remedied by one of thefollowing three methods. The first remedial scheme is to make theturbine run in the over-combustion mode, meaning that a certain extraamount of fuel is combusted in the turbine so that the exhaust gas inthe outlet of the turbine (flowline 6) has a higher temperature than thecompressed air temperature at the inlet of the turbine (flowline 4). Thesecond remedial scheme is to introduce an optional combustion chamber(not shown in FIG. 9 ) in the entry line 4 of the turbine, whichcombusts a certain extra amount of fuel, which increases the temperatureof the compressed air to the highest temperature of the cycle before itenters the turbine. The third, the most fuel-efficient, remedial schemeis to use the waste-heat from the fuel cell to supplement the heatsupply to the primary cycle similar to the second scheme explainedabove.

Further two variations can be obtained as follows. Depending on whetherthe fuel cell operating temperature is low-medium or high, the fuel cellwaste-heat could be injected to the primary cycle either at the flowline3 or at the flowline 4. Similar to the Illustrative Embodiment 5, thispower scheme also can be powered by the liquid hydrogen fuel, thussaving a considerable amount of consumed power in the compressionprocess.

Illustrative Embodiment 7—Hydrogen Driven Brayton-Quasi-isoTT-PATMI(Config I) Power Scheme

This Illustrative Embodiment is an implementation of the Config Iversion of the Brayton-Quasi-isoTT-PATMI shown in FIG. 10 . Incomparison to the Illustrative Embodiment 6 described previously, thefollowing Brayton-isoTT cycle version is easier to implementpractically, because in this Brayton-isoTT version implementation thecombustion of a suitable fuel (such as hydrogen) occurs away from theturbine expander. Consequently, the design of the turbine can be doneindependent to the design of the combustion chambers.

One of the main features of this Illustrative Embodiment is that heatingof the expanding working fluid in the turbine is achieved by injectingmultiple streams of hot working fluid (at T_(max) in the range1000-1200° C.) into the turbine at multiple stages of the expansionprocess, achieving an isothermal expansion that occurs at anear-constant moderate temperature in the range 400-600° C. Thesestreams of hot working fluid are generated in multiple combustionchambers, which are fed with a suitable fuel (such as hydrogen) andstreams of air extracted from the main stream of heated air flowing outof the regenerator. Similar to the PATMI configurations that have beendescribed thus far, all the power-consuming components such ascompressors, are driven by the power generated in a renewable energyfield (not shown in FIG. 10 ).

Workings of the power scheme can be described as follows with referenceto FIG. 10 which depicts only the thermodynamic cycle aspect of thepower scheme. The power scheme extracts atmospheric air at condition(P_(L), T_(L)) through the compressor inlet line 1 and compresses to ahigher pressure P_(H). The compression process is achieved through aseries of compression stages; for example, FIG. 10 shows fourcompression stages. Atmospheric air enters the lowest pressurecompression stage 2 (comp₁), gets compressed to a pressure set by thestage pressure ratio, and leaves the compression stage 2 through theoutlet line 3. The air is directed to the first inter-cooler IC₁ inwhich the air is cooled to a certain degree. The cooled air then entersthe second compression stage 5 through its inlet line 4. The compressionprocess continues progressively when air passes through the remainingcompression stages 5 (comp₂), 8 (comp₃), 11 (comp₄), entering throughtheir individual inlet lines 4, 7, 10 and leaving through theirindividual outlet lines 6, 9, 12. In between the compression stages, theprogressively compressed air is cooled as it passes through theinter-coolers IC₂, IC₃ placed between outlet/inlet lines of thecompression stages, 6/7, 9/10, respectively. Although this IllustrativeEmbodiment is shown with four compression stages in FIG. 10 , in realitythe optimal number of compression stages must be determined to minimizethe total power consumption by compression stages. Further, all thecompression stages are driven by the power generated from a renewableenergy field (not shown in FIG. 10 ), which is independent of the mainpower grid.

Eventually the compressed air, now at its highest pressure P_(H) (whileits temperature is still relatively low due to intercooling, but aboveT_(L)), enters the low-temperature flow passages 30 a of the regenerator30.

The regenerator 30 is a heat exchanger device, which comprises oflow-temperature flow passages 30 a and high-temperature flow passages 30b running approximately in parallel, but in counter-flow directions,facilitates highly effective heat transfer from the high-temperaturefluid stream 30 b to the low-temperature fluid stream 30 a. Thecompressed air enters the low-temperature flow passages 30 a through thecompressor outlet line 12 and is heated to higher temperature by thehigh-temperature working fluid stream, which flows in thehigh-temperature flow passages 30 b. Eventually, the heated compressedair exits the regenerator through the flowline 13.

The high-pressure air, which flows in the flowline 13, is separated intotwo streams 14 and 24, where the first separated major portion of theair flows through the flowline 14 towards the high-pressure expansionstage 15, while the second separated minor portion of the stream isdirected through the flowline 24 to the combustion chamber feedline 25.The objective here is to combust a suitable fuel (such as hydrogen) witha metered portion of air extracted from feedline 25 inside eachcombustion chamber CC₁ through CC₄. The resulting hot combustionproducts (900-1000° C.) streams are then injected into the inlet line ofthe expansion stages so that the major stream of air that enters intoeach expansion stage is heated to the highest temperature T_(H) of thecycle, prior to commencing the expansion process.

For example, referring to the expansion stage 15, a hot air stream isgenerated in the combustion chamber CC₁ by igniting the fuel (hydrogen)with a metered portion of the compressed air extracted from the feedline25, and the generated hot gas stream 25 a is injected to the main airstream 14, thus heating the main air stream 14 to the highesttemperature of the cycle T_(H) prior to entering the expansion stage 15.

Similarly, the hot air/fuel streams 25 b, 25 c, 25 d generated in thecombustion chambers CC₂, CC₃, CC₄ respectively feed the main gas streams16, 18, 20, respectively, prior to entering the expansion stages 17, 19,21, thereby approximating the expansion process to an isothermalexpansion. As shown in FIG. 10 , all the expansion stages are mounted ona single shaft, and the common shaft 50 delivers the power harnessedfrom all expansion stages to drive the AC-electric generators (not shownin FIG. 10 ).

The working fluid air mixed with combustion products, having passedthrough all the expansion stages, attain a pressure very close to thelowest pressure P_(L) of the cycle. It then, exits the final turbinestage 21 through its outlet line 22, and enters the high-temperatureflow passages 30 b of the regenerator 30. Eventually, the exhaust gasstream 22, having passed through the high-temperature flow passages 30 band rejecting its useful heat, leaves the regenerator 30 through thehigh-temperature flow passage outlet line 23. This completes the cycle.

Based on the ideas presented in describing the previous embodiments, anumber of design variances can be proposed here. For example, similar tothe Illustrative Embodiment 5, this power scheme also can be powered bythe liquid hydrogen fuel, thus saving a considerable amount of consumedpower in the compression process. If fuel cells are used in therenewable energy field (not shown in FIG. 10 ) to power the compressorstages, the waste heat of the fuel cell can be fed to the cycle at asuitable location to augment the thermal feed of this embodiment.

Illustrative Embodiment 8—Hydrogen Driven Brayton-Quasi-isoTT-PATMI(Config II) Power Scheme

One drawback of the Illustrative Embodiment 7 described above is that ituses a single high-pressure stream of air (24 of FIG. 10 ) to feed allthe combustion chambers to generate individual hot air streams, whichare in turn injected to the turbine at progressively reducing pressurestages. This causes an energy waste in the compression process as allthe working fluid running through the turbine is compressed to thehighest pressure in the cycle, despite that much of the hot gas isinjected into the expanding gas stream at much lower pressures (flowlines 25 b, 25 c, 25 d in FIG. 10 ). The Illustrative Embodiment 8 isdisclosed to remedy this drawback of the previous configuration, savingsome of the power consumed in the compression process.

The improved implementation of the Config II version of theBrayton-Quasi-isoTT-PATMI is shown in FIG. 11 . Similar to theIllustrative Embodiment 7, this Brayton-isoTT version is easier toimplement practically, since the combustion of a suitable fuel (such ashydrogen) occurs away from the turbine expander. As a result, theturbine can be designed independently without paying any considerationto the design of the combustion chambers and the combustion process.

One of the main features of this Illustrative Embodiment is that heatingof the expanding working fluid in the turbine is achieved by injectingmultiple streams of hot working fluid (at T_(max) 1000-1200° C.) intothe turbine at multiple stages of the expansion process, achieving anapproximate isothermal expansion process that occurs at a near-constantmoderate temperature in the range 400-600° C. However, unlike theIllustrative embodiment 7 where these streams of hot working fluid aregenerated from a single air stream at the highest pressure of the cycle,this Illustrative Embodiment teaches how each of the fuel injecting airstreams are extracted directly from the compression stages at suitablepressure levels. Similar to the PATMI configurations described thus far,all the power consuming components such as compressor stages are drivenby the power generated in a renewable energy field (not shown in FIG. 11). As a result, the total power generated by the turbine stages isdelivered to the AC-electricity generators.

The workings of the power scheme can be described as follows withreference to FIG. 11 , which depicts only the thermodynamic cycle aspectof the power scheme. The power scheme extracts atmospheric air atcondition (P_(L), T_(L)) through the compressor inlet line 1 andcompresses to a higher pressure P_(H). The compression process isachieved through a series of compression stages as shown in FIG. 11 .Although this Illustrative Embodiment is shown with four compressionstages as an example, in reality the optimal number of compressionstages is determined to minimize the total power consumption by all thecompression stages. Atmospheric air enters the lowest pressurecompression stage 2 (comp₁), gets compressed to a pressure set by thestage pressure ratio, and leaves the compression stage 2 through theoutlet flowline 3, which separates the stream into two streams. Out ofthe two separated streams, the first major portion of air passes throughthe first inter-cooler IC₁, while the second minor portion of air isdiverted to the flowline 4. The major stream of air then enters thesecond compression stage 6 through its inlet line 5, while the minorstream of air stream 4 passes through the first set of low-temperatureflow passages 4R of the regenerator 30. The compression processcontinues progressively when air passes through the remainingcompression stages 6 (comp₂), 10 (comp₃), 14 (comp₄), entering throughtheir individual inlet flowlines 5, 9, 13 and leaving through theirindividual outlet flowlines 7, 11, 15.

After the intermediary compression stages 6 and 10, the compressed airoutput streams are individually divided into two streams, out of whichthe first major portions are cooled as they pass through theinter-coolers IC₂, IC₃, while the second minor portions are divertedthrough the flowlines 8 and 12 to a second and a third sets oflow-temperature flow passages 8R and 12R in the regenerator 30. Thecompression process is concluded when the air in the flowline 13 passesthrough the final compression stage 14, which delivers its fullcompressed air output through the flowline 15 to the fourth set oflow-temperature flow passages 15R in the regenerator 30.

The regenerator 30 in this Illustrative Embodiment is a heat exchangerdevice, which comprises of a number (in this case four) oflow-temperature flow passages 4R, 8R, 12R, 15R, and a single set ofhigh-temperature flow passages 30 b running approximately in parallel,but in counter-flow directions, facilitates highly effective heattransfer from the high-temperature fluid stream 30 b to thelow-temperature fluid streams 4R, 8R, 12R, 15R. The regeneration processoccurs when the compressed air streams 4, 8, 12, 15, which are at theirindividual pressures (while its temperature is still relatively low dueto intercooling, but above T_(L)), flow through their individual set oflow-temperature flow passages 4R, 8R, 12R, and 15R and are heated to ahigher temperature by the high-temperature fluid stream that flows inthe high-temperature flow passages 30 b.

The high-pressure air streams which exit from the regenerator throughthe flowline 4 a, 8 a, 12 a, 15 a, are fed into the individualcombustion chamber CC₄, CC₃, CC₂, CC₁ respectively, where meteredamounts of suitable fuel (such as hydrogen) are ignited and burned toform four streams of hot gases 4 b, 8 b, 12 b, 15 b. The resulting hotgas streams are then injected to the main gas streams which pass fromthe consecutive higher-pressure turbine stage to the next lower-pressureturbine stage. For example, the hot gas stream 4 b is injected into thegas stream 21, which flows from the turbine stage 20 to 22. Similarly,the hot gas stream 8 b and 12 b are injected into the gas streams 19 and17 respectively, which flow from the turbine stage 18 to the turbinestage 20 and from 16 to 18 respectively. The only exception is that theturbine expansion stage 16, which operates at the highest pressure, isfed directly by the hot gas stream 15 b generated from the combustionchamber CC₁ and there is no other stream to mix with it. This scheme ofprogressive mixing of the hot gas streams generated by the combustionchambers with the gas streams flowing in between the turbine stages atapproximately equal pressures seems to effectively mimic the isothermalexpansion process.

The working fluid air mixed with combustion products, having passedthrough all the expansion stages, attaining a pressure very close to thelowest pressure of the cycle P_(L), exits the final turbine stage 22through its outlet line 23 and enters the high-temperature flow passages30 b of the regenerator 30. Eventually, the exhaust gas stream 23,having passed through the high-temperature flow passages 30 b leaves theregenerator 30 through the high-temperature flow passage outlet flowline24.

Further, as shown in FIG. 11 , all the compression stages in thisIllustrative Embodiment are driven by the power generated from arenewable energy field (not shown in FIG. 11 ), which is independent ofthe main power grid. As a result, all the power generated in theexpansion stages can be used to drive the AC-electric generators andsupply the main power grid.

Similar to the Illustrative Embodiment 7, this power scheme also couldhave a number of design variances. For example, similar to theIllustrative Embodiment 5, it can be powered by the liquid hydrogenfuel, saving the consumed power in the compression process. Further, iffuel cells are used in the renewable energy field (not shown in FIG. 11) to power the compressor stages, the waste heat liberated in the fuelcells can be fed to the cycle at a suitable location to augment thethermal feed of this embodiment.

Illustrative Embodiment 9—sCO₂-PATMI Schemes for Bottoming CycleApplications

Under the Illustrative Embodiment 3, 4(a), and 4(b) the use of abottoming cycle to recover the waste heat of the main power cycle wasdiscussed and the possible use of the supercritical-CO₂ (sCO₂) cycleschemes was mentioned in this context. In this section, a number of sCO₂schemes are described in detail to demonstrate how they may be convertedto PATMI configurations to improve their efficiencies.

Carbon dioxide gas (CO₂) is detrimental to the environment, and itsrelease into the atmosphere should be prevented at all cost.Nevertheless, CO₂ has tremendous advantages as a power-cycle workingfluid, especially when it is used in the supercritical state. However,there is a caveat; the CO₂ power cycles, being closed cycles, require anadditional cooling heat exchanger to cool the working fluid beforerecycling back to the main compressor.

Illustrative Embodiment 9(a)—sCO₂-PATMI Basic Power Scheme

The basic supercritical-CO₂ (sCO₂) cycle, which is shown in FIG. 12(a)comprises of a compressor 2; a turbine 7; a heat exchanger 15 to heatthe working fluid from the waste-heat source; a heat exchanger 25 tocool the working fluid either by ambient air or a liquid coolant such aswater; and an optional heat exchanger 10 to regenerate a portion of theheat that otherwise would have been wasted.

The workings of the basic cycle are described as follows in reference toFIG. 12(a). The working fluid exists at its lowest pressure and thelowest temperature of the cycles in the flowline 1. The compressor 2extracts the working fluid from the flowline 1, compresses the workingfluid to the highest pressure of the cycle, and delivers the workingfluid to the compressor delivery line 3. The working fluid flows alongthe flowline 3 to the low-temperature flow passages 10 a of theregenerator 10, where the pressurized fluid is heated to a certaindegree.

The regenerator 10, in effect a heat exchanger device, which comprisesof low-temperature flow passages 10 a and high-temperature flow passages10 b running approximately in parallel, but in counter-flow directions,facilitates highly effective heat transfer from the high-temperaturefluid stream 10 b to the low-temperature fluid stream 10 a.

The heated working fluid leaves the regenerator 10 through the flowline4 to the main waste-heat exchanger 15 where the fluid is heated to thehighest temperature of the cycle. The working fluid, which is now at itshighest pressure and the highest temperature of the cycle, enters theturbine 7 through the turbine inlet flowline 6. In the turbine 7, theworking fluid expands while the turbine rotors harness the mechanicalpower from the expanding working fluid, and the generated power isdelivered through the turbine shaft 30 to drive the AC-electricgenerators (not shown in FIG. 12(a)).

The expanded working fluid, now at its lowest pressure, exits theturbine through the flowline 8 and enters the high-temperature flowpassages 10 b of the regenerator 10. In the regenerator 10 the workingfluid rejects heat thus lowering its temperature to a certain degree,and exits the regenerator through the flowline 9. The working fluidflows through the flowline 9 to the cooling heat exchanger 25 to becooled to the lowest temperature of the cycle. Eventually, the cooledworking fluid, now at its lowest pressure and its lowest temperatureleaves the cooling heat exchanger through the flowline 1, thuscompleting the cycle.

In this PATMI power scheme, the compressor is driven by the powergenerated in a renewable energy field, such as solar PV, wind turbines,and/or power generated by fuel cell technology. Consequently, the totalpower generated in the turbine 7 is used to drive the AC-electricgenerators to supply power to the main power grid. Further, if there arefuel cells in the renewable energy field, which provide DC-electricpower, a portion of the fuel cells' waste heat can supplement thethermal feed of the sCO₂ power scheme.

Despite its simplicity, the basic sCO₂ cycle is not a highly efficientpower cycle. Therefore, various flow schemes, some of which with addedcomplexity, are used to increase the efficiency of the sCO₂ power cycle.The next few sections describe some of these more complex sCO₂ basedpower schemes, while demonstrating how they could adopt the PATMItechnology to improve their operating efficiencies.

Illustrative Embodiment 9(b)—sCO₂-PATMI Split-Flow Recompression Scheme

This Illustrative Embodiment for an sCO₂-PATMI power scheme, whichcomprises of two compressor stages in parallel, a single turbine, andtwo-stage regeneration, is commonly known as the Split-FlowRecompression Scheme. The workings of this particular sCO₂ scheme can bedescribed as follows in reference to FIG. 12(b). The main compressor 2(Comp₁) extracts the cooled working fluid (CO₂ in supercritical state)through the main compressor feedline 1, compresses the working fluid tothe highest pressure of the cycle, and delivers the compressed workingfluid to the flowline 3. The working fluid flows along the flowline 3 tothe first low-temperature regenerator 10, and then along the flowline 4to the second high-temperature regenerator 20.

The regenerator 10 (and 20), in effect a heat exchanger device, whichcomprises a set of low-temperature flow passages 10 a (and 20 a) and aset of high-temperature flow passages 10 b (and 20 b) runningapproximately in parallel, but in counter-flow directions, facilitateshighly effective heat transfer from the high-temperature fluid stream 10b (and 20 b) to the low-temperature fluid stream 10 a (and 20 a).

The compressed working fluid, which enters the low-temperature flowpassages 10 a of the regenerator 10, is heated to a certain hightemperature by the high-temperature fluid stream, which flows in thehigh-temperature flow passages 10 b. The heated compressed working fluidexits the regenerator 10 through the flowline 4. The compressed workingfluid that flows in the flowline 4, mixes with the recompressed workingfluid which flows along the flowline 16, and the mixed stream flowsalong the flowline 5 to the high-temperature regenerator 20. The workingfluid, which enters the low-temperature flow passages 20 a of theregenerator 20, is further heated by the high-temperature stream whichflows in the high-temperature flow passages 20 b. The heated fluidstream exits the flow passages 20 a through the flowline 6.

The flowline 6 delivers the pressurized working fluid, now heated to ahigher degree, to the main waste-heat exchanger 15, where the workingfluid is heated to the highest temperature of the cycle. The heatedworking fluid flows to the turbine 8 through the flowline 7. In theturbine the working fluid expands to the lowest pressure of the cycle,allowing the turbine rotors to harness the mechanical power of theexpanding working fluid. Eventually, the mechanical power harnessed inthe turbine is delivered through its shaft 30 to drive the AC-electricgenerators (not shown in FIG. 12(b)), and the expanded working fluidleaves the turbine through the flowline 9.

The flowline 9 delivers the low-pressure working fluid to thehigh-temperature flow passages 20 b of the high-temperature regenerator20, where the working fluid is cooled as it rejects heat to the flowpassages 20 a. The cooled working fluid leaves the high-temperatureregenerator through the flowline 11. The flowline 11 delivers thelow-pressure working fluid to the high-temperature flow passages 10 b ofthe low-temperature regenerator 10, where the working fluid is furthercooled. The working fluid, now at a moderate-to-low temperature, leavesthe low-temperature regenerator through the flowline 12. The fluidstream 12 is then split into two separate streams, and the first splitstream flows through the flowline 13 a to the cooling heat exchanger 25,while the second split stream flows through the flowline 13 b to thecompressor 14 for recompression.

In the cooling heat exchanger 25, the fluid stream 13 a is cooled to thelowest temperature of the cycle and so cooled fluid stream leavescooling heat exchanger through the main compressor feedline 1. The fluidstream, which flows in the flowline 13 b is recompressed to the maximumpressure, while the temperature of the fluid stream also is raised to acertain degree. Eventually, the compressed fluid stream is delivered tothe flowline 16, to complete the cycle.

Similar to the other PATMI power schemes described previously, thecompressors in this Illustrative Embodiment are driven by theDC-electric power generated by a renewable energy field which may alsoinclude fuel cells. Consequently, the total power generated by theturbine drives the AC-electric generators to supply power to the mainpower grid. Further, if there are fuel cells in the renewable energyfield, which provide DC-electric power, a portion of the waste heat fromthe fuel cells can augment the thermal feed of the sCO₂ scheme.

Illustrative Embodiment 9(c)—sCO₂-PATMI Partial Compression RegenerationScheme

This Illustrative Embodiment for an sCO₂-PATMI power scheme, whichcomprises of two compressors in series, a single turbine, and two-stageregeneration, is commonly known as the Partial Compression Regenerationscheme. The workings of this particular sCO₂ scheme can be described asfollows in reference to FIG. 12(c). The low-pressure compressor 2(Comp₁) extracts the working fluid, which is at its lowest pressure ofthe cycle through the flowline 1, compresses the working fluid to asuitable intermediate pressure for the cycle, and delivers the partiallycompressed working fluid to the flowline 3. The partially compressedworking fluid flows along the flowline 3 to the first low-temperatureregenerator 10.

The regenerator 10 (and 20), in essence a heat exchanger device, whichcomprises a set of low-temperature flow passages 10 a (and 20 a) and aset of high-temperature flow passages 10 b (and 20 b) runningapproximately in parallel, but in counter-flow directions, facilitateshighly effective heat transfer from the high-temperature fluid stream 10b (and 20 b) to the low-temperature fluid stream 10 a (and 20 a).

The partially compressed working fluid flows through thehigh-temperature flow passages 10 b of the regenerator 10 and conveysheat to the low-temperature passages 10 a of the regenerator. Thepartially compressed fluid stream, which is now cooled to a certaindegree, leaves the regenerator flow passages 10 b through the flowline4, and flows to the cooling heat exchanger 25. The cooling heatexchanger 25 cools the partially compressed working fluid to the lowesttemperature of the cycle and delivers the working fluid to the secondcompressor stage 6 (Comp₂) through the compressor feedline 5. The secondcompressor 6 compresses the working fluid to the highest pressure of thecycle and delivers to the compressor outlet line 7, which conveys theworking fluid to the low-temperature flow passages 10 a of theregenerator 10.

The high-pressure working fluid stream, which flows in thelow-temperature flow passages 10 a of the regenerator 10, is heated to acertain degree by the high-temperature fluid stream that flows in thehigh-temperature flow passages 10 b. The heated working fluid leaves theregenerator 10 through the flowline 8 and enters the low-temperatureflow passages 20 a of the regenerator 20, where it is further heated bythe high-temperature stream which flows in the high-temperature flowpassages 20 b.

The high-pressure working fluid leaves the low-temperature flow passages20 a of the regenerator 20 through the flowline 9 and enters the mainwaste-heat exchanger 15, where the working fluid is heated to thehighest temperature of the cycle. The working fluid, now at the highestpressure and the temperature of the cycle, flows through the flowline 11to the turbine stage 12, where it expands to the lowest pressure of thecycle enabling the turbine rotors to harness the mechanical power.

Eventually, the mechanical power harnessed in the turbine is deliveredthrough the turbine shaft 30 to drive the AC-electric generators (notshown in FIG. 12(c)), while the expanded working fluid leaves theturbine through the flowline 13. The flowline 13 delivers thelow-pressure working fluid through the high-temperature flow passages 20b of the high-temperature regenerator 20 enabling the working fluid tocool to a certain degree. The cooled fluid stream leaves the regenerator20 through the flowline 1 to be compressed by the compressor 2, thuscompleting the cycle.

Similar to the other PATMI power schemes described previously, thecompressors in this Illustrative Embodiment are driven by theDC-electric power generated by a renewable energy field which may alsoinclude fuel cells. Consequently, the total power generated by theturbine is used to drive the AC-electric generators to supply power tothe main power grid. Further, if there are fuel cells in the renewableenergy field, which provide DC-electric power, a portion of the wasteheat from the fuel cells can augment the thermal feed of the sCO₂scheme.

Illustrative Embodiment 9(d)—sCO₂-PATMI Partial Cooling RecompressionScheme

This Illustrative Embodiment for an sCO₂-PATMI power scheme, whichcomprises of three compressors, a single turbine, two-stage cooling, andtwo-stage regeneration, is commonly known as the Partial CoolingRecompression scheme. The scheme differs from the previously describedschemes as it comprises of three compressors and two cooling stages. Thescheme is devised by placing the two high-pressure compressor stages inparallel while the single low-pressure compression stage in seriesrelative to the high-pressure compressor stages.

The workings of this particular sCO₂ scheme are described as follows inreference to FIG. 12(d). The first stage cooling heat exchanger 25delivers the working fluid, which is at the lowest pressure and lowesttemperature of the cycle, to the main compressor stage 2 through themain compressor feedline 1. The main compressor stage 2 compresses theworking fluid to a suitable intermediate pressure for the cycle anddelivers to the flowline 3. The working fluid stream 3 is then splitinto two separate parallel streams, where the first split stream 4enters the second stage cooling heat exchanger 35 to be further cooled,while the second split stream 21 enters the recompression stage 22 to becompressed to the highest pressure of the cycle. The second splitstream, having gone through the recompression process, eventually flowsthrough the flowline 23 to be mixed with the first split stream.

The first split stream, which is cooled by the second stage cooling heatexchanger 35, enters the second compressor stage 6 (Comp₂) through itsfeedline 5, and is compressed to the highest pressure of the cycle. Thefluid stream, now at the highest pressure of the cycle, flows throughthe compressor delivery line 7 to the low-temperature regenerator 10.

The regenerator 10 (and the regenerator 20), in effect a heat exchangerdevice, which comprises a set of low-temperature flow passages 10 a (and20 a) and a set of high-temperature flow passages 10 b (and 20 b)running approximately in parallel, but in counter-flow directions,facilitates highly effective heat transfer from the high-temperaturefluid stream 10 b (and 20 b) to the low-temperature fluid stream 10 a(and 20 a).

The compressed first split fluid stream, which enters thelow-temperature flow passages 10 a of the regenerator 10, is heated to acertain higher temperature by the high-temperature fluid stream, whichflows in the high-temperature flow passages 10 b. The heated workingfluid exits the regenerator 10 through the flowline 8. The two splitstreams, which emerge through the flowlines 8 and 23, now at the highestpressure of the cycle, mix together and the mixed stream flows along theflowline 9 to the high-temperature regenerator 20. The mixed stream ofworking fluid, which flows in the low-temperature flow passages 20 a, isfurther heated by the high-temperature stream that flows in thehigh-temperature flow passages 20 b. The heated fluid stream exits theflow passages 20 a through the flowline 11.

The flowline 11 delivers the pressurized working fluid, now heated to ahigher degree, to the main waste-heat exchanger 15, where it is heatedto the highest temperature of the cycle. The working fluid, now at thehighest temperature of the cycle, flows through the flowline 12 to theturbine stage 13, where it expands to the lowest pressure of the cycle,enabling the turbine rotors to harness the mechanical power from theexpanding working fluid. The mechanical power harnessed in the turbineis delivered through the shaft 30 to drive the AC-electric generators,while the expanded working fluid leaves the turbine through the flowline14.

The flowline 14 delivers the low-pressure working fluid to thehigh-temperature regenerator 20, where the working fluid rejects heatflowing through the high-temperature flow passages 20 b of theregenerator. The working fluid, having cooled in the regenerator 20,leaves the high-temperature flow passages 20 b through the flowline 16.The flowline 16 delivers the low-pressure working fluid to thehigh-temperature flow passages 10 b of the low-temperature regenerator10, and the working fluid stream is further cooled. Eventually, theworking fluid leaves the flow passages 10 b through the flowline 17. Thecycle is completed when the fluid stream 17 enters the first-stagecooling heat exchanger 25 to be cooled to the lowest temperature of thecycle.

Similar to the other PATMI power schemes described previously, the threecompressors in this Illustrative Embodiment are driven by theDC-electric power generated by a renewable energy field, which may alsoinclude fuel cells. Consequently, the total power generated by theturbine is used to drive the AC-electric generators to supply power tothe main power grid. Further, if there are fuel cells in the renewableenergy field, which provide DC-electric power, a portion of the wasteheat from the fuel cells can augment the thermal feed of the sCO₂scheme.

Illustrative Embodiment 9(e)—sCO₂-PATMI Two-Stage Compression andTwo-Stage Heating Scheme

This Illustrative Embodiment for an sCO₂-PATMI power scheme, whichcomprises of two compressors, two-stage cooling, two-stage heating, andsingle turbine is commonly known as the Two-stage Compression withTwo-stage Heating scheme. This scheme differs from the previouslydescribed schemes as this scheme comprises of a low-temperature and ahigh-temperature heating stages.

The workings of this particular sCO₂ scheme are described as follows inreference to FIG. 12(e). The first stage cooling heat exchanger 25delivers the working fluid at the lowest pressure and the lowesttemperature of the cycle, to the main compressor 2 (Comp₁) through themain compressor feedline 1. The main compressor 2 compresses the workingfluid to a suitable intermediate pressure for the cycle, and deliversthe compressed working fluid to the second stage cooling heat exchanger35, which is in effect an intercooler, through the flowline 3. Theworking fluid, having cooled in the second cooling heat exchanger 35,flows through the flowline 4 and enters the second stage compressor 5(Comp₂), where it is compressed to the highest pressure of the cycle.The second stage compressor 5 delivers the high-pressure working fluidto the flowline 6, which is then split into two separate parallelstreams 7 a and 7 b. The first split stream 7 a enters thelow-temperature flow passages 10 a in the regenerator 10 in the scheme,while the second split stream 7 b enters the low-temperature waste-heatexchanger 15 a to be heated to a certain high temperature. The secondsplit stream, having gone through the low-temperature heating process,leaves the low-temperature waste-heat exchanger 15 a through theflowline 8 b.

The regenerator 10, in effect a heat exchanger device, which comprises aset of low-temperature flow passages 10 a and a set of high-temperatureflow passages 10 b running approximately in parallel, but incounter-flow directions, facilitates highly effective heat transfer fromthe high-temperature fluid stream 10 b to the low-temperature fluidstream 10 a. The first split fluid stream 7 a enters the low-temperatureflow passages 10 a of the regenerator 10 and is heated to a certainhigher temperature by the high-temperature fluid stream, which flows inthe high-temperature flow passages 10 b of the regenerator. The heatedcompressed working fluid exits the flow passages 10 a through theflowline 8 a.

The two split streams, which emerge through the flowlines 8 a and 8 b,now at the highest pressure of the cycle and at a certain hightemperature, undergo mixing, and the mixed stream flows along theflowline 9 to the main (high-temperature) waste-heat exchanger 15 b. Inthe waste-heat exchange the working fluid is heated to the highesttemperature of the cycle, and the heated working fluid flows to theturbine stage 12 through the flowline 11. In the turbine the workingfluid expands to the lowest pressure of the cycle, enabling the turbinerotors to harness the mechanical power of the expanding working fluid.The mechanical power harnessed in the turbine is delivered through itsshaft 30 to drive the AC-electric generators (not shown in FIG. 12(e)),while the expanded working fluid leaves the turbine through the flowline13.

The flowline 13 delivers the low-pressure working fluid to thehigh-temperature flow passages 10 b of the regenerator 10, where thefluid stream rejects heat and cools down. Eventually, working fluidleaves the flow passages 10 b through the flowline 14. The cycle iscompleted when the fluid stream 14 enters the first-stage cooling heatexchanger 25 to be cooled to the lowest temperature of the cycle.

Similar to the other PATMI power schemes described previously, the threecompressors in this Illustrative Embodiment are driven by theDC-electric power generated by a renewable energy field which may alsoinclude fuel cells. Consequently, the total power generated by theturbine is used to drive the AC-electric generators to supply power tothe main power grid. Further, if there are fuel cells in the renewableenergy field, which provide DC-electric power, a portion of the wasteheat from the fuel cells can augment the thermal feed of the sCO₂scheme.

Illustrative Embodiment 9(f)—sCO₂-PATMI Two Parallel Turbines (Config I)Scheme

This Illustrative Embodiment for an sCO₂-PATMI power scheme is aconfiguration with two turbines in parallel. It comprises of a singlecompressor, two turbines placed in parallel, and two-stage regeneration,is commonly known as the Two Parallel Turbine scheme (Config I). Theworkings of this particular sCO₂ scheme can be described as follows inreference to FIG. 12(f). The compressor 2 (Comp) extracts the workingfluid, which is at its lowest pressure and its lowest temperature of thecycle, through the flowline 1; compresses the working fluid to thehighest pressure of the cycle; and delivers the compressed working fluidto the flowline 3. The flow stream 3 is then split into two separateparallel streams 4 and 14. The first split stream 4 enters thewaste-heat exchanger 15 to be heated to the highest-temperature of thecycle, while the second split stream 14 is directed to the first-stageregenerator 10.

This scheme comprises of two regenerators 10 and 20 to rejuvenate theheat that otherwise would have wasted. The regenerator 10 (and 20) is inessence a heat exchanger device, which comprises a set oflow-temperature flow passages 10 a (and 20 a) and a set ofhigh-temperature flow passages 10 b (and 20 b) running approximately inparallel, but in counter-flow directions, so that the design facilitateshighly effective heat transfer from the high-temperature fluid stream 10b (and 20 b) to the low-temperature fluid stream 10 a (and 20 a).

The high-pressure working fluid, which flows in the flowline 14 entersthe low-temperature flow passages 10 a of the first-stage regenerator10, and is heated to a certain degree by the high-temperature fluidstream which flows through the high-temperature flow passages 10 b ofthe regenerator. The heated working fluid leaves the regenerator flowpassages 10 a through the flowline 16 and enters the low-temperatureflow passages 20 a of the second-stage high-temperature regenerator 20.The working fluid flows in the flow passages 20 a is further heated bythe high-temperature stream, which flows in the high-temperature flowpassages 20 b.

Eventually, the high-pressure working fluid leaves the flow passages 20a of the regenerator 20 through the flowline 17 and enterslow-temperature turbine 18. In the turbine 18 the working fluid expandsto the lowest pressure of the cycle, allowing the turbine rotors toharness the mechanical power of the expanding working fluid. Theexpanded working fluid, now at the lowest pressure of the cycle, leavesthe turbine 18 through the turbine outlet line 19.

The first split stream 4, which is heated to the highest temperature ofthe cycle by the waste-heat exchanger 15, enters the high-temperatureturbine 7 through the turbine feedline 6. In the turbine the workingfluid expands to the lowest pressure of the cycle, enabling the turbinerotors to harness the mechanical power of the expanding working fluid.Eventually, the mechanical power harnessed by both turbines is deliveredthrough their common shaft 30 to drive the AC-electric generators (notshown in FIG. 12(f)).

It is noteworthy that the output stream of the turbine 7 has a highertemperature than the temperature of the output stream of the turbine 18.The difference stems from the fact that the working fluid feed 6 to theturbine 7 is heated by the heat source, which in this case is thewaste-heat from a high-temperature primary cycle, whereas the workingfluid feed 17 of the turbine 18 is heated by the regenerator 20.Consequently, only the output stream of the turbine 7 is hot enough toregenerate heat in the high-temperature regenerator 20. Therefore, thehot output stream 8 of the turbine 7 flows through the high-temperatureflow passages 20 b of the regenerator 20, to regenerate heat to the flowstream 20 a. The working fluid stream 20 b leaves the regenerator 20through the flowline 9 to merge with the other parallel stream 19.

The flow streams 9 and 19 are at the lowest pressure of the cycle andthey also will be of similar low temperatures. The two working fluidstreams are mixed, and the mixed stream 11 enters high-temperature flowpassages 10 b of the regenerator 10, which further regenerates heat tothe high-pressure flow stream 10 a. Eventually, the low-pressure workingfluid stream leaves the regenerator 10 through the flowline 12 andenters the cooling heat exchanger 25. In the cooling heat exchanger 25the working fluid is cooled to the lowest temperature of the cycle to befed into the flowline 1. This completes the cycle.

Similar to the other PATMI power schemes described previously, thecompressor in this Illustrative Embodiment is driven by the DC-electricpower generated by a renewable energy field which may also include fuelcells. Consequently, the total power generated by the turbine is used todrive the AC-electric generators to supply power to the main power grid.Further, if there are fuel cells in the renewable energy field, whichprovide DC-electric power, a portion of the waste heat from the fuelcells can augment the thermal feed of the sCO₂ scheme.

Illustrative Embodiment 9(g)—sCO₂-PATMI Two Parallel Turbines (ConfigII) Scheme

This Illustrative Embodiment for an sCO₂-PATMI power scheme is anotherconfiguration with two turbines in parallel. It comprises of a singlecompressor, two turbines placed in parallel, and two-stage regeneration,is commonly known as the Two Parallel Turbine scheme (Config II). Theworkings of this particular sCO₂ scheme can be described as follows inreference to FIG. 12(g). The compressor 2 (Comp) extracts the workingfluid, which is at its lowest pressure and its lowest temperature of thecycle, through the flowline 1; compresses the working fluid to thehighest pressure of the cycle; and delivers the compressed working fluidto the flowline 3. The flow stream 3 is directed to the first-stageregenerator 10.

This scheme comprises of two regenerators 10 and 20 to rejuvenate theheat otherwise would have wasted. The regenerator 10 (and 20) is inessence a heat exchanger device, which comprises a set oflow-temperature flow passages 10 a (and 20 a) and a set ofhigh-temperature flow passages 10 b (and 20 b) running approximately inparallel, but in counter-flow directions, so that the design facilitateshighly effective heat transfer from the high-temperature fluid stream 10b (and 20 b) to the low-temperature fluid stream 10 a (and 20 a).

The high-pressure working fluid, which flows in the flowline 3 entersthe low-temperature flow passages 10 a of the first-stage regenerator10, and is heated to a certain degree by the high-temperature fluidstream which flows through the high-temperature flow passages 10 b ofthe regenerator. The heated working fluid leaves the regenerator flowpassages 10 a through the flowline 4, which is then split into twoseparate parallel streams 5 and 14. The first split stream 5 enters thewaste-heat exchanger 15 to be heated to the highest-temperature of thecycle, while the second split stream 14 is directed to the second-stageregenerator 20. The flow stream 14 enters the low-temperature flowpassages 20 a of the second-stage high-temperature regenerator 20. Theworking fluid is further heated by the high-temperature stream whichflows in the high-temperature flow passages 20 b.

Eventually, the high-pressure working fluid leaves the flow passages 20a of the regenerator 20 through the flowline 17 and enterslow-temperature turbine 18. In the turbine 18 the working fluid expandsto the lowest pressure of the cycle, allowing the turbine rotors toharness the mechanical power of the expanding working fluid. Theexpanded working fluid, now at the lowest pressure of the cycle, leavesthe turbine 18 through the turbine outlet line 19.

The first split stream 4, which is heated to the highest temperature ofthe cycle by the waste-heat exchanger 15, enters the high-temperatureturbine 7 through the turbine feedline 6. In the turbine the workingfluid expands to the lowest pressure of the cycle, enabling the turbinerotors to harness the mechanical power of the expanding working fluid.Eventually, the mechanical power harnessed by both turbines is deliveredthrough their common shaft 30 to drive the AC-electric generators (notshown in FIG. 12(g)).

It is noteworthy that the output stream of the turbine 7 has a highertemperature than the temperature of the output stream of the turbine 18.The difference stems from the fact that the working fluid feed 6 to theturbine 7 is heated by the heat source, which in this case is thewaste-heat from a high-temperature primary cycle, whereas the workingfluid feed 17 of the turbine 18 is heated by the regenerator 20.Consequently, only the output stream of the turbine 7 is hot enough toregenerate heat in the high-temperature regenerator 20. Therefore, thehot output stream 8 of the turbine 7 flows through the high-temperatureflow passages 20 b of the regenerator 20, to regenerate heat to the flowstream 20 a. The working fluid stream 20 b leaves the regenerator 20through the flowline 9 to merge with the other parallel stream 19.

The flow streams 9 and 19 are at the lowest pressure of the cycle andthey also will be of similar low temperatures. The two working fluidstreams are mixed, and the mixed stream 11 enters high-temperature flowpassages 10 b of the regenerator 10, which further regenerates heat tothe high-pressure flow stream 10 a. Eventually, the low-pressure workingfluid stream leaves the regenerator 10 through the flowline 12 andenters the cooling heat exchanger 25. In the cooling heat exchanger 25the working fluid is cooled to the lowest temperature of the cycle to befed into the flowline 1. This completes the cycle.

Similar to the other PATMI power schemes described previously, thecompressor in this Illustrative Embodiment is driven by the DC-electricpower generated by a renewable energy field which may also include fuelcells. Consequently, the total power generated by the turbine is used todrive the AC-electric generators to supply power to the main power grid.Further, if there are fuel cells in the renewable energy field, whichprovide DC-electric power, a portion of the waste heat from the fuelcells can augment the thermal feed of the sCO₂ scheme.

Illustrative Embodiment 10—PATMI Power Generation Scheme with a FuelCell Driven Combined Compressor/Generator and a Turbine Driven Generator

Many Illustrative Embodiments presented thus far contained a fuel cellwhich generates DC electricity to operate the compressors. In some ofthese cases the fuel cell also provided a part of the heat required forthe gas-turbine power cycle to operate. However, in the IllustrativeEmbodiments previously presented, the fuel cell is in essence depictedas a heat exchanger to transfer heat to the working fluid of thegas-turbine power cycle without being explicit as to how the fuel cellis fed with fuel and air. The Illustrative Embodiments 10 through 23show how a fuel cell can be integrated to the gas-turbine power cycle sothat the fuel cell operates at a pressure higher than the atmosphericpressure while the fuel cell consumes the high-pressure air supplied bythe compressor(s) of the gas-turbine power cycle. In turn, the fuel cellprovides the electricity to power the compressor(s) while it also expelsa hot flue gas stream, and possibly a hot air stream to the gas-turbinepower cycle, thus providing a part of the heat requirement of thegas-turbine power cycle.

FIG. 13 shows one of the basic Illustrative Embodiments where a singlecompressor, a single turbine, and a fuel cell can be integrated to forma single stage PATMI power scheme. Its workings can be described asfollows. The compressor C₁ extracts atmospheric air from the air intake1, compresses air to a higher pressure, and delivers the air stream tothe high-pressure flow passage 2. The heat exchangers LT-HX and HT-HXwhich regenerate heat from the flue gas, operate in the low-temperaturerange and in the high-temperature range respectively. These devices areplaced in series so that the compressed air stream is heated as it flowsfrom the flow passage 2 to the flow passage 3 through the heat exchangerLT-HX and then flows from the flow passage 3 a to the flow passage 5through the heat exchanger HT-HX.

In this Illustrative Embodiment the fuel cell FC is possibly ahigh-temperature fuel cell such as the SOFC type, which can be poweredwith a variety of gaseous fuels including ammonia, syngas, natural gas,methane, or hydrogen. Here the focus is on a syngas powered SOFC fuelcell, as syngas neither requires reformation nor requires preheatingsince syngas is typically produced from an incineration process. Thefuel cell FC consists of two electrodes (see FIG. 13 ); the cathode andthe anode. While the anode is fed with the hot (600-800° C.) syngas asthe fuel, through the flow passage A, the cathode is fed with hot(700-800° C.) compressed air from the heat exchanger HT-HX through theflow passage 5. The gaseous fuel and the oxygen in the compressed airreact electrochemically within the high-temperature electrolyte(500-1,000° C.) of the fuel cell, and a portion of the fuel undergoesoxidation while the fuel cell produces electricity. As a result, hotpartially oxidized fuel exits the anode through the flow passage D,while the hot compressed air with less oxygen exits the cathode throughthe flow passage E. The two streams D and E are mixed into apost-combustor PC, where the unreacted fuel completes the oxidationreaction, thereby producing a high-temperature flue gas stream, whichexits the post-combustor PC through the flow passage 7. The temperatureof the stream 7 depends on the fuel utilization factor of the fuel cellFC; the lower the fuel utilization in the fuel cell, the higher would bethe temperature of the flue gas stream. For example, according to onepublished source², 30-50% fuel utilization can increase the mixed streamtemperature to values as high as 1800-1350° C., whereas at 70-80% fuelutilization can lower the temperature to about 1080-850° C. 2. FuelUtilization Effects On System Efficiency In SOFC-Gas Turbine HybridSystems; Oryshchyn, D., Harun, N. F., Tucker, D., Bryden, M. C., Shadle,L.; Applied Energy (2018), 228, 1953-1965

The bypassed compressed air stream 4 (so named since it bypasses thehigh-temperature heat exchanger HT-HX), which is extracted from the flowpassage 3 will be at a certain temperature, somewhat higher than thetemperature of the stream 2, but lower than that of the stream 5. Thebypassed compressed air stream 4 and the hot flue gas stream 7 are fedinto a static mixing device M₁, where the two streams mix andhomogenize. The resulting mixed stream 8 is fed to the single turbine inthe system T₁. The mixed stream 8 expands while flowing through theturbine T₁. As a result, the turbine rotors harness mechanical power,which is delivered through the turbine shaft. The turbine T₁ in turndrives the generator G₂, and the generator, possibly a synchronous type,delivers AC electricity to the main power grid. The expanded workingfluid exits the turbine T₁ through the flow passage 9, and then itenters the high-temperature heat exchanger HT-HX to reject heat. The hotflue gas stream flows through the heat exchanger HT-HX rejecting heat,thereby heating the compressed air stream, which flows from flow passage3 a to flow passage 5. The flue gas stream then exits thehigh-temperature heat exchanger HT-HX through the flow passage 10, whichdirects the flue gas stream into the low-temperature heat exchangerLT-HX. The flue gas stream flows through the heat exchanger LT-HXrejecting heat further and eventually exits the heat exchanger LT-HXthrough the flow passage 11, which allows the flue gas stream to escapeto the atmosphere, thereby dissipating the low-temperature heat contentof the stream.

In par with the previous PATMI Illustrative Embodiments presented here,the compressor C₁ is driven by the electric motor 40, which in turn ispowered by the electricity generated by the fuel cell FC. In a typicalscenario, as shown in FIG. 13 , the fuel cell is capable of producingelectricity in excess of the electricity consumed by the compressor.Therefore, to harness the excess electricity produced by the fuel cell,a generator G₁, possibly an induction-type AC generator, is mounted onthe same shaft of the compressor/motor combination as shown in FIG. 13 .A battery bank 100 may be used to accommodate the imbalance of the fuelcell electric power supply and the power consumption of the electricmotor which drives the compressor/generator combination.

Illustrative Embodiment 11—Two-Stage PATMI Power Generation Scheme witha by-Pass Cooling Air Stream and a High-Pressure Turbine Cycle

FIG. 14 shows another version of a fuel cell integrated PATMIgas-turbine power scheme. However, in this case the gas-turbine powerscheme is a two-stage scheme consisting of a low-pressure (first stage)power cycle and a high-pressure (second stage) power cycle. Here, thelow-pressure power cycle resembles the Illustrative Embodiment 10 to ahigh degree. Further, the high-pressure second-stage power cycle isdriven by the heat rejected by the first-stage power cycle. The workingsof the power scheme can be described as follows.

The low-pressure compressor stage LPC extracts atmospheric air from itsintake line 1 and compresses air to a pressure just above the operatingpressure of the fuel cell FC. The low-pressure compressor stage deliversthe partially compressed air, now at a temperature somewhat higher thanthe ambient temperature, to the flow passage 2. The air stream 2 is thensplit into two streams, one of which is cooled as it passes through theinter-cooler IC and then enters the intake line 13 of the high-pressurecompressor stage HPC. The other stream 2 a enters the low-pressure,low-temperature heat exchanger LP-LT-HX to be heated by the regeneratedheat. As shown in FIG. 14 , the low-pressure stream 2 a is heatedregeneratively as it passes through the two counter-flow heat exchangersLP-LT-HX and LP-HT-HX, which are placed in series. The compressed airstream 2 a is heated as it passes through the low-temperaturefirst-stage heat exchanger LP-LT-HX by the relatively cooler flue gasstream which flows from the flow passage 10 to the flow passage 11. Theheated low-pressure compressed air stream then exits the heat exchangerthrough the flow passage 3. The compressed air stream 3 is then splitinto two streams, one of which flows through the by-pass flow passage 4,and the other stream 3 a is further heated as it passes through thehigh-temperature second-stage heat exchanger LP-HT-HX by the relativelyhotter flue gas stream which flows from the flow passage 9 to the flowpassage 10. This heated low-pressure compressed air stream is fed to thecathode of the fuel cell FC through the flow passage 5. The fuel, inthis case hot syngas, generated from an incineration process andsubsequently filtered to remove all undesirable constituents, is fed tothe anode of the fuel cell FC through the flow passage A.

In the high-temperature electrolyte of the fuel cell FC, the gaseousfuel and the oxygen in the low-pressure compressed air stream reactelectrochemically, and a portion of the fuel undergoes oxidation whilethe fuel cell produces electricity. Subsequently, hot partially oxidizedfuel exits the anode through the flow passage D, while the hotcompressed air with less oxygen exits the cathode through the flowpassage E. The two streams D and E are mixed into a post-combustor PC,where the fuel is allowed to complete the oxidation reaction. Theresulting high-temperature flue gas stream exits the post-combustor PCthrough the flow passage 7. As mentioned in reference to theIllustrative Embodiment 10, the temperature of the stream 7 depends onthe fuel utilization factor of the fuel cell FC. The mixed hot flue gasstream 7 and the by-pass compressed air stream 4 are then combined andmixed in a static mixing device M₁ to form a mixed stream 8 a. Thestream 8 a is then fed to the heat exchanger HP-HT-HX to harness aportion of its heat content to the high-pressure power cycle. The stream8 a, having been cooled in the heat exchanger HP-HT-HX to a certaindegree, leaves the heat exchanger through the flow passage 8. The fluegas stream 8 enters the low-pressure turbine LPT, where the streamexpands to a lower pressure close to the atmospheric pressure allowingthe turbine rotors to harness the mechanical power. The power harnessedby the turbine rotors drives the electric generator G₁, which convertsthe mechanical power output of the turbine to electricity. Eventually,the flue gas, now at a pressure very close to the atmospheric pressure,leaves the turbine through the flow passage 9 and the stream passesthrough the heat exchangers LP-HT-HX and LP-LT-HX, in that sequence,passing through the flow passages 10 and 11 to regeneratively heat thecounter-flow compressed air stream 2 a to produce the hot air stream 5.The low-pressure power cycle completes when the flue-gas stream expelsitself to the atmosphere through the flow passage 11.

The high-pressure power cycle begins as the partially compressed airstream 13 enters the high-pressure compression stage HPC, which furthercompresses the air stream 13 to a much higher pressure (800-1,000 kPa).The high-pressure compressor stage expels the high-pressure air streamthrough the flow passage 14 to the first-stage regenerative heatexchanger HP-LT-HX. In this heat exchanger, the compressed air stream 14is heated to a certain high temperature from the hot air stream flowingin the counter-flow direction from the flow passage 16 to flow passage17. The heated high-pressure air stream then enters the second-stageregenerative heat exchanger HP-HT-HX through the flow passage 141. Thehigh-pressure air stream 141 is further heated as it passes through thisheat exchanger by the counter-flow flue-gas stream in the low-pressurepower cycle which flows from the flow passage 8 a to the flow passage 8.Eventually, the heated high-pressure stream leaves heat exchangerHP-HT-HX through the flow passage 15 and enters the high-pressure stageturbine HPT. In the turbine the high-pressure air expands to a pressuresomewhat higher than the atmospheric pressure allowing the turbinerotors to harness the mechanical power. The turbine rotors drive asecond electric generator G₂ which converts the mechanical power feed ofthe turbine to an electrical power output. The expanded air stream exitsthe high-pressure turbine stage through the flow passage 16, whichdirects the stream to the regenerative heat exchanger HP-LT-HX. The airstream eventually leaves the high-pressure power cycle through the flowpassage 17 completing the high-pressure power cycle.

In accordance with the previous PATMI Illustrative Embodiments presentedhere, the compressor LPC and HPC are driven by the electric motor 40,which in turn is powered by the electricity generated by the fuel cellFC. A battery bank 100 may be used to accommodate the imbalance of thefuel cell electric power supply and the power consumption of theelectric motors. One noteworthy aspect in this Illustrative embodimentis that the high-pressure power cycle is an externally-heated cycle,meaning that the working fluid remains pure air without any fuelcombustion occurring in the cycle. Another noteworthy aspect is thatsince the by-pass stream 4 inevitably cools the output stream 7 of thepost combustor PC, this configuration is more appropriate for scenarioswhere the fuel cell fuel utilization factor is relatively low, whichmakes the temperature of the flue gas stream 7 relatively high.

Illustrative Embodiment 12—Two-Stage PATMI Power Generation Scheme withan Auxiliary Combustor in the by-Pass Air Stream and a High-PressureTurbine Cycle

With reference to the Illustrative Embodiment 11, it was highlightedthat the power scheme (see FIG. 14 ) is more suitable for scenarioswhere the temperature of the output flue gas stream 7 of thepost-combustor is relatively high. The Illustrative Embodiment 12covered here, on the contrary, is more suitable for scenarios where thetemperature of the output flue gas stream of the post-combustor ismoderately high, meaning that the heat content of the mixed stream 8 ais not adequate to drive the high-pressure power cycle. Therefore, adesign change is required to convey more heat into the flue gas stream 8a.

As shown in FIG. 15 , Illustrative Embodiment 12 remedies thisinadequacy by incorporating an auxiliary combustor AC in the by-pass airstream 4. As a result, the temperature of the flue gas stream 8 a can beincreased by controlling the rate of fuel combustion in the saidauxiliary combustor AC. Apart from this minor modification, theIllustrative Embodiment 12 performs more or less the same manner as theIllustrative Embodiment 11.

Illustrative Embodiment 13—Two-Stage PATMI Power Generation Scheme withTwo Auxiliary Combustors and a High-Pressure Turbine Cycle with aThermal Feed to a Bottoming Cycle

With reference to the Illustrative Embodiment 12, it was highlightedthat the power scheme (see FIG. 15 ) is more suitable for scenarioswhere the temperature of the output flue gas stream 7 of thepost-combustor is moderately high. The Illustrative Embodiment 13covered here, on the contrary, is more suitable for scenarios where thetemperature of the output flue gas stream of the post-combustor isrelatively low. The typical scenario here is that the heat content ofthe mixed stream 8 a is not only insufficient, but also this inadequacycannot be remedied merely by incorporating the auxiliary combustor AC(see FIG. 15 ), even if the temperature of the by-pass air stream israised to the maximum practically possible value. This scenario warrantsa further design modification to the high-pressure power cycle, and thatis to incorporate a second auxiliary combustor AC₂ at the inlet of thehigh-pressure turbine. However, the incorporation of a second auxiliarycombustor provides further advantages in terms of harnessing more power.For example, since the added second auxiliary combustor enables thecontrolling of the inlet temperature of the high-pressure turbine, itfacilitates the incorporation of a third bottoming cycle driven by theheat from the high-pressure power cycle. The details of the resultingpower scheme can be described as follows.

The low-pressure cycle of this Illustrative Embodiment operates exactlythe same as the low-pressure cycle in the Illustrative Embodiments 12;therefore, the operation of the low-pressure cycle will not be describedhere. The high-pressure cycle begins (see FIG. 16 ) when the split airstream 13 undergoes the second-stage compression process in thehigh-pressure compressor stage HPC. The high-pressure compressor HPCfurther compresses the air stream 13 to a much higher pressure comparedto the fuel cell operation pressure. The high-pressure compressor stageexpels the high-pressure air stream through the flow passage 14 to thefirst-stage regenerative heat exchanger HP-LT-HX. In this heatexchanger, the compressed air stream 14 is heated to a certain hightemperature from the hot air stream flowing in the counter-flowdirection from the flow passage 16 a to flow passage 17. The heatedhigh-pressure air stream then enters the second-stage regenerative heatexchanger HP-HT-HX through the flow passage 141. The high-pressure airstream 141 is further heated as it passes through this heat exchangerfrom the heat rejected by the counter-flow flue-gas stream in thelow-pressure power cycle, which flows from the flow passage 8 a to theflow passage 8. Eventually, the heated high-pressure air stream leavesthe heat exchanger HP-HT-HX through the flow passage 15 and enters thehigh-pressure auxiliary combustor AC₂. In the auxiliary combustor AC₂, asuitable fuel is combusted, and the air stream temperature increases toa certain degree, at which point the air stream becomes a flue gasstream due to the combustion products introduced. Heated flue gas streamthen enters the high-pressure stage turbine HPT through the turbineinlet passage 15 a. In the turbine, the high-pressure air stream expandsto a pressure somewhat higher than the atmospheric pressure, allowingthe turbine rotors to harness the mechanical power. The turbine drives asecond electric generator G₂ thereby converting the mechanical powerfeed of the turbine to an electrical power output. The expanded flue gasstream exits the high-pressure turbine stage through the flow passage16, which directs the flue gas stream to the regenerative heat exchangerHP-BC-HX, which feeds the excessive heat in the post-expanded flue gasstream to a thermally-coupled third bottoming cycle 90. The flue gasstream, having been cooled to a certain degree due rejection of heat todrive the bottoming cycle 90, leaves the heat exchanger HP-BC-HX throughthe flow passage 16 a and enters the low-temperature regenerative heatexchanger HP-LT-HX. In the heat exchanger HP-LT-HX, the flue gas stream16 a further cools rejecting heat and eventually leaves thehigh-pressure power cycle through the flow passage 17, completing thehigh-pressure power cycle.

In accordance with the previous PATMI Illustrative Embodiments presentedhere, the compressor LPC and HPC are driven by the electric motor 40,which in turn is powered by the electricity generated by the fuel cellFC. A battery bank 100 may be used to accommodate the imbalance of thefuel cell electric power supply and the power consumption of theelectric motors.

Illustrative Embodiment 14—Two-Stage PATMI Power Generation Scheme wherethe Low-Pressure Turbine is Fed with the Combined Exhaust from the FuelCell and the High-Pressure Turbine Cycle

This Illustrative Embodiment is also a two-stage power generating schemelike the Illustrative Embodiments 11 through 13; however, it differsfrom the others in terms of the pressure ratio of the high-pressurecycle turbine. In this Illustrative Embodiment, the high-pressure cyclehot gas stream expands in two stages, first through the high-pressureturbine stage and then through the low-pressure turbine stage.Consequently, the low-pressure turbine power capacity increases due tothe increase in the mass flow rate through it. Accordingly, the heatcapacity of the hot gas stream, which preheats the fuel cell air feed isalso increased. The workings of this Illustrative Embodiment can bedescribed as follows in reference to FIG. 17 .

The low-pressure compressor stage LPC extracts the atmospheric air fromits intake line 1 and compresses air to a pressure just above theoperating pressure of the fuel cell FC. The low-pressure compressorstage delivers the partially compressed air, now at a temperaturesomewhat higher than the ambient temperature, to the flow passage 2. Thecompressed air stream 2 is then split into two streams, one of which iscooled as it passes through the inter-cooler IC and then enters theintake line 23 of the high-pressure compressor stage HPC. The othercompressed air stream 2 a enters the low-pressure, low-temperature heatexchanger LP-LT-HX to be heated by the regenerated heat harnessed fromthe flue gas stream. As shown in FIG. 17 , the low-pressure stream 2 ais heated regeneratively as it passes through the two counter-flow heatexchangers LP-LT-HX and LP-HT-HX, which are placed in series. Thecompressed air stream 2 a is first heated as it passes through thelow-temperature first-stage heat exchanger LP-LT-HX by the relativelycooler flue gas stream which flows from the flow passage 14 to the flowpassage 15. The partially heated compressed air stream then enters thehigh-temperature second-stage heat exchanger LP-HT-HX to be furtherheated by the relatively hotter flue gas stream which flows from theflow passage 12 to the flow passage 13.

This heated low-pressure compressed air stream is fed to the cathode ofthe fuel cell FC through the flow passage 5. The fuel, in this case hotsyngas generated from an incineration process and subsequently filteredto remove all undesirable constituents, is fed to the anode of the fuelcell FC through the flow passage A. In the high-temperature electrolyteof the fuel cell FC, the gaseous fuel and the oxygen in the low-pressurecompressed air stream react electrochemically, and a portion of the fuelundergoes oxidation while the fuel cell produces electricity. As aresult, hot partially oxidized fuel exits the anode through the flowpassage D, while the hot compressed air with less oxygen exits thecathode through the flow passage E. The two streams D and E are mixedinto a post-combustor PC, where the remaining fuel in the stream D isallowed to complete the oxidation reaction. The resultinghigh-temperature flue gas stream exits the post-combustor PC through theflow passage 7. As mentioned in reference to the Illustrative Embodiment10, the temperature of the stream 7 depends on the fuel utilizationfactor of the fuel cell FC. The hot flue gas stream 7 enters the heatexchanger HP-HT-HX to harness a portion of its heat content to thehigh-pressure power cycle. The stream 7, having been cooled in the heatexchanger HP-HT-HX to a certain degree, leaves the heat exchangerthrough the flow passage 8.

The high-pressure power cycle begins as the partially compressed airstream 23 enters the high-pressure compression stage HPC, which furthercompresses the air stream 23 to a much greater pressure. Thehigh-pressure compressor stage expels the high-pressure air streamthrough the flow passage 24 to the first-stage high-pressureregenerative heat exchanger HP-LT-HX. In this heat exchanger, thecompressed air stream 24 is heated to a certain high temperature fromthe hot flue gas stream flowing in the counter-flow direction from theflow passage 13 to flow passage 14. The heated high-pressure air streamthen enters the second-stage regenerative heat exchanger HP-HT-HXthrough the flow passage 25. The high-pressure air stream 25 is furtherheated as it passes through this counter-flow heat exchanger HP-HT-HX bythe flue-gas stream of the low-pressure power cycle, which flows fromthe flow passage 7 to the flow passage 8. Eventually, the heatedhigh-pressure air stream leaves heat exchanger HP-HT-HX through the flowpassage 26 and enters the high-pressure stage turbine HPT. In theturbine, the high-pressure air stream expands to a pressure somewhatclose to the low-pressure turbine LPT inlet pressure, allowing theturbine rotors to harness the mechanical power. The turbine rotors drivea second electric generator G₂, which converts the mechanical power feedof the turbine to an electrical power output. The expanded air streamexits the high-pressure turbine stage HPT through the flow passage 28.

The hot air stream 28 which is now at a pressure close to that of theflue gas stream 8 are mixed and the mixed hot gas stream 11 enters tothe low-pressure stage turbine LPT. In the low-pressure turbine LPT, themixed hot gas stream expands to a lower pressure close to theatmospheric pressure allowing the turbine rotors to harness themechanical power. The power harnessed by the turbine rotors drives theelectric generator G₁, which converts the mechanical power output of theturbine to electricity. Eventually, the hot gas stream, now at apressure very close to the atmospheric pressure, leaves the turbinethrough the flow passage 12 and enters the regenerative heat exchangersLP-HT-HX where the stream transfers heat to raise the temperature of thelow-pressure compressed air stream 3. The hot gas stream leaves the heatexchanger LP-HT-HX through the flow passage 13 and enters thecounter-flow heat exchanger HP-LT-HX, where it transfers heat further toraise the temperature of the high-pressure compressed air stream 24.Finally, the hot gas stream leaves the heat exchanger HP-LT-HX throughthe flow passage 14, which directs the hot gas stream to thelow-temperature, counter-flow heat exchanger LP-LT-HX. In thelow-temperature heat exchanger LP-LT-HX, the hot gas stream regeneratesits low-temperature heat content raising the temperature of therelatively cooler low-pressure air stream 2 a. The low-pressure andhigh-pressure power cycles are complete when the hot gas stream leavesthe low-temperature heat exchanger LP-LT-HX and expels itself to theatmosphere through the flow passage 15.

In accordance with all the PATMI power generating schemes presented thusfar, the compressors in this combined cycle are driven by an electricmotor 40, which is in turn driven by the electricity produced by thefuel cell FC in the primary cycle, possibly with a battery bank 100 tostore electricity. The battery bank 100 accommodates the imbalance ofthe fuel cell electric power supply and the power consumption of theelectric motor.

Illustrative Embodiment 15—Two-Stage PATMI Power Generation Scheme withThree Auxiliary Combustors and a Bottoming Cycle Driven by a ThermalFeed from the High-Pressure Cycle

This Illustrative Embodiment is also a two-stage power generatingscheme, which can be seen as a hybrid version of the IllustrativeEmbodiments 13 and 14. Illustrative Embodiment 13 presented previouslyhas two auxiliary combustors and a bottoming cycle, which is thermallyfed by the high-pressure cycle. In comparison, this IllustrativeEmbodiment has three auxiliary combustors and a bottoming cycle, whichis also thermally fed by the high-pressure cycle. However, in theIllustrative Embodiment 13, the expansion of the high-pressure cycleflue gas stream occurs completely to a near-atmospheric pressure in thehigh-pressure turbine, quite independently of the low-pressure turbine.As a result, the flue gas streams of both cycles expel themselves to theatmosphere through two different regenerative heat exchangers. Incomparison in this Illustrative Embodiment, the high-pressure turbinecauses the high-pressure cycle flue gas to expand partially until thestream pressure approaches the inlet pressure of the low-pressureturbine, thereafter the flue gasses of both cycles form a mixed streamto expand through the low-pressure turbine, similar to the IllustrativeEmbodiment 14.

The workings of this Illustrative Embodiment can be described asfollows. As FIG. 18 shows, the low-pressure compressor stage LPCextracts atmospheric air from its intake line 1 and compresses air to apressure just above the operating pressure of the fuel cell FC. Thelow-pressure compressor stage delivers the partially compressed air, nowat a temperature somewhat higher than the ambient temperature, to theflow passage 2. The air stream 2 is then split into two streams, one ofwhich is cooled as it passes through the inter-cooler IC and then entersthe intake line 13 of the high-pressure compressor stage HPC. The otherstream 2 a enters the low-pressure, low-temperature heat exchangerLP-LT-HX to be heated by the regenerated heat. As shown in FIG. 18 , thelow-pressure stream 2 a is heated regeneratively as it passes throughthe two counter-flow heat exchangers LP-LT-HX and LP-HT-HX, which areplaced in series. The compressed air stream 2 a is heated as it passesthrough the low-temperature first-stage heat exchanger LP-LT-HX by therelatively cooler flue gas stream which flows from the flow passage 10to the flow passage 11. The heated low-pressure compressed air streamthen exits the heat exchanger through the flow passage 3. The compressedair stream 3 is then split into two streams, one of which flows throughthe by-pass flow passage 4, and the other stream 3 a is further heatedas it passes through the high-temperature second-stage heat exchangerLP-HT-HX by the relatively hotter flue gas stream which flows from theflow passage 9 to the flow passage 10. The heated low-pressurecompressed air stream is then fed to the cathode of the fuel cell FCthrough the flow passage 5. The fuel, in this case hot syngas generatedfrom an incineration process and subsequently filtered to remove allundesirable constituents, is fed to the anode of the fuel cell FCthrough the flow passage A.

In the high-temperature electrolyte of the fuel cell FC, the gaseousfuel and the oxygen in the low-pressure compressed air stream reactelectrochemically, and a portion of the fuel undergoes oxidation whilethe fuel cell produces electricity. As a result, hot partially oxidizedfuel exits the anode through the flow passage D, while the hotcompressed air with less oxygen exits the cathode through the flowpassage E. The two streams D and E are mixed into a post-combustor PC,where the fuel is allowed to complete the oxidation reaction. Theresulting high-temperature flue gas stream exits the post-combustor PCthrough the flow passage 7. As mentioned in reference to theIllustrative Embodiment 10, the temperature of the stream 7 depends onthe fuel utilization factor of the fuel cell FC.

The by-pass air stream 4 is further split into two streams, the firstportion of which flows along the flow passage 41 and is heated bycombusting a suitable fuel in the first auxiliary combustor AC₁. Theresulting flue gas stream leaves the auxiliary combustor AC₁ through theflow passage 41 a. The second portion of the split air stream 4 flowsthrough the flow passage 42, which is also heated by combusting asuitable fuel in the third auxiliary combustor AC₃. The resulting fluegas leaves the third auxiliary combustor AC₃ through the flow passage 42a.

The hot flue gas stream 7 and the heated first by-pass compressed airstream 41 a are then combined to form the mixed stream 8 a in a staticmixing device M₁. The stream 8 a is then fed to the heat exchangerHP-HT-HX to harness a portion of its heat content to the high-pressurepower cycle. The stream 8 a, having been cooled in the heat exchangerHP-HT-HX to a certain degree, leaves the heat exchanger through the flowpassage 8 b. At this point the low-pressure cycle flue gas stream 8 b iscombined with the high-pressure cycle flue gas stream to form a mixedstream, thus the description will be focused on the workings of thehigh-pressure cycle.

The high-pressure power cycle begins as the partially compressed airstream 13 enters the high-pressure compression stage HPC, which furthercompresses the air stream 13 to a much higher pressure. Thehigh-pressure compressor stage expels the high-pressure air streamthrough the flow passage 14 to the regenerative heat exchanger HP-HT-HXwhere the high-pressure air stream is heated by the low-pressure cycleflue gas stream flowing from the flow passage 8 a to the flow passage 8b. The heated high-pressure air stream then enters the second auxiliarycombustor AC₂ through the flow passage 15. In the auxiliary combustorAC₂, the high-pressure air stream is further heated by combusting asuitable fuel. The resulting hot flue gas stream 15 a leaves theauxiliary combustor AC₂ and enters the high-pressure stage turbine HPT.In the turbine, the high-pressure hot flue gas stream expands to apressure slightly higher than the inlet pressure of the low-pressureturbine LPT, allowing the turbine rotors to harness the mechanicalpower. The turbine rotors drive a second electric generator G₂ whichconverts the mechanical power feed of the turbine to an electrical poweroutput. The expanded flue gas stream exits the high-pressure turbinestage through the flow passage 16 and enters the regenerative heatexchanger HP-BC-HX, which acts as a thermal feed to a suitably coupledbottoming cycle 90. In order to get the best performance, this bottomingcycle should be of a Rankine (steam) cycle type or a sCO₂ cycle type.The flue gas stream eventually leaves the bottoming cycle heat exchangerHP-BC-HX through the flow passage 16 a, which is then mixed with thesecond flue gas stream 42 a emitting from the third auxiliary combustorAC₃ to form the hot flue gas mix stream 17.

The mixed flue gas stream 17 is in turn mixed with the low-pressurecycle flue gas stream 8 b, and the resulting mixed stream 8 enters thelow-pressure turbine LPT. In the low-pressure turbine LPT, the combinedflue gas stream 8 expands to a lower pressure close to the atmosphericpressure, allowing the turbine rotors to harness the mechanical power.The power harnessed by the turbine rotors drives the electric generatorG₁, which converts the mechanical power output of the turbine toelectricity. Eventually, the flue gas, now at a pressure very close tothe atmospheric pressure, leaves the low-pressure turbine LPT throughthe flow passage 9 and the stream passes through the heat exchangersLP-HT-HX and LP-LT-HX, in that sequence, passing through the flowpassages 10 and 11 to regeneratively heat the counter-flow compressedair stream 2 a. The low-pressure and the high-pressure cycles conclude,once the flue gas stream 11 expels itself to the atmosphere.

In accordance with all the PATMI power generating schemes presented thusfar, the compressors in this combined cycle are driven by an electricmotor 40, which is in turn driven by the electricity produced by thefuel cell FC in the low-pressure cycle, possibly with a battery bank 100to store electricity. The battery bank 100 accommodates the imbalance ofthe fuel cell electric power supply and the power consumption of theelectric motor. A noteworthy aspect of this two-stage power generatingscheme is that having three auxiliary combustors enable the achievementof the preferable temperature levels at temperature critical pointswhile maintaining the maximum temperature to not to exceed a limitingvalue (say 1200° C.). For example, for this combined-cycle to perform asintended, the temperature of the streams 5, 15 a, and 16 should havelower-bound temperature values. To achieve these limiting temperatures,the fluid streams 9, 8 a, and 15 a should have the corresponding minimumlimits. These temperature conditions can be easily met having the threeindependent auxiliary combustors in the system.

Illustrative Embodiment 16—Two-Stage PATMI Power Generation Scheme witha Fuel-Feed, a Steam-Feed, a Reformer, and Fuel Preheaters

This Illustrative Embodiment differs from the Illustrative Embodiments10 through 15 as it comprises a gaseous fuel feed, a water/steam feed,and a reformer/pre-reformer. In this Illustrative Embodiment, thegaseous fuel is fed through two flow circuits which operate at twopressure levels. The first is a low-pressure fuel feed to drive thelow-pressure power cycle, that also includes the fuel cell. The secondis a high-pressure fuel feed to power the high-pressure power cycle. Theworkings of this two-stage power scheme can be described as follows withreference to FIG. 19 . Since this Illustrative Embodiment has twoauxiliary flow layouts for a gaseous fuel (such as natural gas) feed anda water/steam feed, in addition to the two power cycle layouts, it isworthwhile to describe the operation of the two auxiliary layouts beforedescribing the operation of the main power cycles.

The electric motor 403 drives a water pump which pumps atmospheric waterextracted from the water supply line 31 to the high-pressure waterdelivery line 32. The high-pressure water flows through the waterpreheater/boiler heat exchanger HX₆ where the water is converted tohigh-pressure steam. The generated steam is fed through the flow line 33to a fuel/steam mixer M where the high-pressure steam is mixed with agaseous high-pressure fuel.

The two-stage fuel compressor, which is driven by an electric motor 402,comprises a low-pressure compression stage 20 a and a high-pressurecompression stage 20 b. The low-pressure compressor stage 20 a extractsthe gaseous fuel from the fuel supply line 21 and compresses the fuel tothe low-pressure fuel delivery line 22. A portion of this compressedfuel is delivered to the low-pressure power cycle through the flowpassage 23, while the remainder is further compressed by thehigh-pressure compressor stage 20 b and is delivered to thehigh-pressure fuel delivery line 26. The high-pressure fuel deliveryline 26 passes through the first high-pressure fuel preheater HX₄ andthen flows through the flow passage 27 to enter the second high-pressurefuel preheater HX₁ where the high-pressure fuel stream is further heatedbefore the fuel stream enters the high-pressure combustor C₁ through theflow passage 28.

The low-pressure fuel line 23 passes through the first low-pressure fuelpreheater HX₅, and so heated fuel is delivered to the secondlow-pressure fuel preheater HX₂ through the fuel flow passage 24. Theheated fuel stream leaves the second fuel reheater HX₂ through the flowpassage 25, which is then split into two streams 25 a and 25 b. The fuelstream 25 a enters the low-pressure combustor C₂, while the other fuelstream 25 b enters the fuel/steam mixer M where the fuel stream is mixedwith the high-pressure steam fed through the steam line 33. The mixedstream 34 enters the reformer REF, where the fuel/steam mixtureundergoes the reformation reaction producing a significant amount ofhydrogen. Since the reformation reaction is endothermic, the requiredheat for the reaction may be provided to the reformer REF by therecirculation of the fuel stream through the optional recirculation path34 a. The partially reformed fuel enters the fuel cell anode through theflow passage 35.

The two-stage main cycles begin when the atmospheric air is extracted bythe two-stage compressor through the air supply line 1, and the air iscompressed in the first stage compressor to a pressure slightly higherthan the pressure at which the fuel cell SOFC operates. The firstcompressor stage delivers the low-pressure compressed air to the flowpassage 2. The compressed air stream 2 is then split into two streams,the first of which is delivered to the flow passage 2 a to be used inthe low-pressure cycle. The second split stream is cooled through theinter-cooler IC and delivered to the inlet flow passage 13 of thehigh-pressure compressor stage where air is further compressed to a muchhigher pressure to be used in the high-pressure cycle.

The high-pressure cycle continues when the high-pressure compressorstage delivers air to the flow passage 14. The high-pressure compressedair stream 14 enters the high-pressure regenerator REG where thecompressed air stream is heated by the hot flue gas stream whichcounter-flows from the flow passage 41 to flow passage 42. The heatedair stream 15 enters the high-pressure combustor C₁ where itstemperature is further increased due to the combustion of the fuelstream 28. The resulting very hot flue gas stream 16 enters thehigh-pressure turbine stage HPT where the high-pressure hot flue gasstream expands to a pressure slightly higher than the inlet pressure ofthe low-pressure turbine LPT, allowing the turbine rotors to harness themechanical power. The expanded flue gas stream exits the high-pressureturbine stage through the flow passage 17 which directs the flue gasstream to mix with the flow stream 38 to form a combined stream 38 a.

The low-pressure cycle continues when the low-pressure air stream entersthe first low-pressure air preheater HX₃ where the air is heated to acertain temperature. The air stream leaves the first low-pressurepreheater through the flow passage 3 which is split into two streams 3 aand 3 b. The first split low-pressure air stream 3 a enters the cathodeof the fuel cell SOFC to power the fuel cell, while the second splitlow-pressure air stream 3 b enters low-pressure combustor C₂ where thefuel fed through the fuel line 25 a undergoes the combustion reaction toform a hot flue gas stream 4 b.

In the high-temperature electrolyte of the fuel cell SOFC, the gaseousfuel stream 35 and the oxygen in the low-pressure compressed air stream3 a react electrochemically, and a major portion of the fuel undergoesoxidation while the fuel cell produces electricity. As a result, hotpartially oxidized fuel exits the anode through the flow passage 36,while the hot compressed air with less oxygen exits the cathode throughthe flow passage 4 a. The two streams 4 a and 36 are mixed into apost-combustor FC-PC, where the fuel completes the oxidation reaction.The resulting high-temperature flue gas stream exits the post-combustorFC-PC through the flow passage 37. The hot flue gas streams 37 and 4 bwhich emits from the low-pressure combustor are combined to form themixed stream 38. As previously mentioned, the flue gas streams 38 and 17are further combined to form a single stream 38 a. The combined flue gasstream 38 a enters the low-pressure turbine stage LPT where the combinedflue gas stream expands to a lower pressure close to the atmosphericpressure, allowing the turbine rotors to harness the mechanical power.As shown in FIG. 19 , both turbine stages can be mounted on the sameshaft to drive a single generator G, which converts the mechanical powerfeed of the two turbine stages to an electrical power output. It shouldbe mentioned here that the workings of the two cycles will not besignificantly altered if the two turbine stages were to drive twoseparate generators.

The expanded flue gas, now at a pressure slightly higher than theatmospheric pressure, leaves the low-pressure turbine stage LPT throughthe flow passage 39 which directs the flue gas stream to pass throughthe second high-pressure fuel preheater HX₁ where the fuel stream 28 ispreheated. The flue gas stream, having passed through the secondhigh-pressure fuel preheater HX₁, enters the high-pressure airregenerator REG through the flow passage 41 where much of the heatcontent of the flue gas stream is used up to regeneratively heat thehigh-pressure compressed air stream 14. The flue gas stream leaves thehigh-pressure air regenerator REG through the flow passage 42, whichdirects the flue gas stream to pass through the rest of the regenerativeheat exchanges: the second low-pressure fuel preheater HX₂; thelow-pressure air preheater HX₃; the first high-pressure fuel preheaterHX₄; the first low-pressure fuel preheater HX₅; and the water boilerHX₆, in that sequence, directed by the flow passages 43, 44, 45, and 46respectively. Eventually, the flue gas stream expels itself to theatmosphere through the flue passage 47, thus completing the two-stagepower cycle.

In accordance with all the PATMI power generating schemes presented thusfar, the compressors and pumps in this combined cycle are driven by theelectric motors 401, 402, and 403, which are in turn driven by theelectricity produced by the fuel cell SOFC, possibly with a battery bank100 to store electricity. The battery bank 100 accommodates theimbalance of the fuel cell electric power supply and the powerconsumption of the electric motors.

Illustrative Embodiment 17—Two-Stage PATMI Power Generation Scheme witha Reformer Fed with Steam Generated Using the Exhaust of High-PressureGas Turbine Cycle

This Illustrative Embodiment is almost identical to the IllustrativeEmbodiment 16 described previously, except that it differs in the waythe steam is generated to feed the fuel cell. Therefore, thisdescription is provided only to explain the workings of the water/steamcircuit in reference to FIG. 20 .

The electric motor 403 drives a water pump 30 which pumps atmosphericwater extracted from the water supply line 31 to the high-pressure waterdelivery line 32. The high-pressure water flows through the waterpreheater/boiler heat exchanger HX₆ where the water is preheated. Thepreheated water leaves the preheater HX₆ through the flow line 33 andenters the steam generator/superheater STM-HX. In the heat exchangerSTM-HX, the water is converted to steam, as it absorbs the heat rejectedby the flue gas stream which enters from the flow passage 39 and exitsthrough the flow passage 39 a. One noteworthy feature here is that sincethe steam is generated by the heat regenerated by the flue gas, theamount of water that can be converted to steam is substantially highercompared to the same in the Illustrative Embodiment 16. It, therefore,enables the generation of more steam than what is consumed by the fuelcell, and this excess steam can now be used to generate extra powerpassing through a turbine.

The generated steam exits the heat exchanger STM-HX through the flowpassage 33 a. A portion of the steam so generated branches off throughthe flow passage 33 b and enters the low-pressure turbine stage LPT. Inthe turbine, the injected steam, mixed with the expanding flue gas,produces extra power, enhancing the power output of the low-pressureturbine stage LPT. The remainder of the stream 33 a is fed to thefuel/steam mixer M so that the two cycles continue as described withreference to the Illustrative Embodiment 16.

Illustrative Embodiment 18—Two-Stage PATMI Power Generation Scheme witha High-Pressure Gas Turbine Cycle where Turbine Blades are Cooled bySteam

This Illustrative Embodiment is a further extension of the IllustrativeEmbodiments 16 and 17 described previously. In this IllustrativeEmbodiment, the mass flow rate through the heat exchanger STM-HX isfurther increased so that a portion of the water fed through thesteam-generating heat exchanger could be used to cool thehigh-temperature blades in the high-pressure turbine stage. This designfeature enables the high-pressure turbine inlet temperature to be raisedto a higher value, thus gaining an added advantage in the systemperformance. Since the workings of this Illustrative Embodiment aresimilar to the workings of the Illustrative Embodiment 16 to a higherdegree, the description is restricted only to the workings of thewater/steam circuit in reference to FIG. 21 .

The electric motor 403 drives a water pump 30 which pumps atmosphericwater extracted from the water supply line 31 to the high-pressure waterdelivery line 32. The high-pressure water flows through the waterpreheater/boiler heat exchanger HX₆ where the water is preheated. Thepreheated water leaves the preheater HX₆ through the flow line 33 andenters the steam generator/superheater STM-HX. In the heat exchangerSTM-HX, the water is converted to steam, as it absorbs the heat rejectedby the flue gas stream which enters from the flow passage 39 and exitsthrough the flow passage 39 a. The generated steam exits the heatexchanger STM-HX through the flow passage 33 a. A portion of the steamso generated, branches off through the flow passage 33 b and enters theturbine blade-cooling passages in the high-pressure turbine stage HPT,where the steam is further heated while the turbine blades are cooled.The heated steam, now in a superheated-steam state, leaves thehigh-pressure turbine stage HPT through the flow passage 33 c, whichdirects the steam to enter the low-pressure turbine stage HPT at asuitably chosen entry-port. In the low-pressure turbine stage LPT, thesteam expands mixed with the expanding flue gas enabling the turbinestage LPT to harness extra power. The remainder of the stream 33 a isfed to the fuel/steam mixer M so that the two cycles continue, asdescribed with reference to the Illustrative Embodiment 16.

The two most significant advantages of this Illustrative Embodiment overthe Illustrative Embodiment 17 are that:

-   -   (1) due to the incorporation of blade-cooling in the        high-pressure turbine stage HPT, it can operate at a        considerably higher inlet temperature, which increases the        maximum temperature of the high-pressure cycle, thus enhancing        the performance of the high-pressure cycle; and    -   (2) the inlet steam temperature as well as the mass flow rate to        the low-pressure turbine stage LPT is considerably increased due        to the heat extracted by blade-cooling, thus enhancing the        performance of the low-pressure cycle.

Illustrative Embodiment 19—Two-Stage PATMI Power Generation Scheme withPre-Reformer/Reformer and Three Regenerative Heat Exchangers in theHigh-Pressure Gas Turbine Cycle

This Illustrative Embodiment differs from Illustrative Embodiments 10through 18 since this Illustrative Embodiment has three regenerativeheat exchangers in the high-pressure cycle and a water/steam separatorin the low-pressure cycle. The workings of this Illustrative Embodimentshown in FIG. 22 , can be described as follows. The description firstconcentrates on the high-pressure water supply and the gaseous fuelsupply circuits.

The electric motor 403 drives a water pump which pumps atmospheric waterextracted from the water supply line 31 to the high-pressure waterdelivery line 32. The high-pressure water flows through the waterpreheater/boiler heat exchanger WAT-HX where the water is converted tohigh-pressure steam with a low dryness-fraction. The generated steam isfed through the flow passage 33 to a steam/water separator SEP, wheredry-steam and water are separated. The separated dry-steam leaves theseparator through the flow passage 33 a, while the separated waterleaves the separator SEP through the flow passage 33 b. The flow passage33 a directs the stream of dry-steam 33 a to the fuel/steam mixer M,where the high-pressure steam is mixed with the pressurized gaseousfuel.

The two-stage fuel compressor, which is driven by an electric motor 402,comprises a low-pressure compression stage 20 a and a high-pressurecompression stage 20 b. The low-pressure compressor stage 20 a extractsthe gaseous fuel from the fuel supply line 21 and compresses the gaseousfuel to the low-pressure fuel delivery line 22. A portion of thiscompressed fuel is delivered to the low-pressure power cycle through theflow passage 23, while the remainder is further compressed by thehigh-pressure fuel compressor stage 20 b and is delivered to thehigh-pressure fuel delivery line 26. The high-pressure fuel deliveryline 26 passes through the high-pressure fuel preheater HP-FL-HX andthen flows through the flow passage 27 to enter the high-pressurecombustor C₁ where the fuel is mixed and combusted with thehigh-pressure compressed air stream that enters through the flow passage17.

The low-pressure fuel line 23 passes through the first low-pressure fuelpreheater LP-FL-HX1, and so heated fuel is delivered to the secondlow-pressure fuel preheater LP-FL-HX2 through the fuel flow passage 24.The heated fuel stream leaves the second fuel reheater LP-FL-HX2 throughthe flow passage 25 and enters the fuel/steam mixer M, where the fuelstream is mixed with the high-pressure steam, that is fed through thesteam line 33 a. The mixed stream 51 enters the reformer/pre-reformerREF, where the fuel/steam mixture undergoes the reformation reactionproducing a significant amount of hydrogen. Since the reformationreaction is endothermic, the required heat for the reaction may beprovided to the reformer REF by the recirculation of thepartially-oxidized anode outlet stream 53 through the optionalrecirculation path 53 a. The partially reformed fuel enters the fuelcell anode through the flow passage 52.

The two-stage main cycles begin when the atmospheric air is extracted bythe two-stage compressor through the air supply line 1, and the air iscompressed in the first stage compressor LPC to a pressure slightlyhigher than the pressure at which the fuel cell SOFC operates. The firstcompressor stage LPC delivers the low-pressure compressed air to theflow passage 2. The compressed air stream 2 is then split into twostreams, the first of which is delivered to the flow passage 2 a to beused in the low-pressure cycle. The second split stream is cooledthrough the inter-cooler IC and delivered to the inlet flow passage 13of the high-pressure compressor stage HPC, where the air stream isfurther compressed to a much higher pressure to be used in thehigh-pressure cycle.

The high-pressure cycle continues when the high-pressure compressorstage HPC delivers air to the flow passage 14. The high-pressurecompressed air stream 14 enters the first high-pressure air heatregenerator HP-LT-HX where the compressed air stream is heated by thehot flue gas stream which flows in the counter-flow direction from theflow passage 56 to flow passage 57. The heated high-pressure air stream15 is further heated in the second and third high pressure air heatregenerators HP-HT-HX1 and HP-HT-HX2 consecutively, passing through theflow passage 16 connecting the two heat regenerators. The heatedhigh-pressure air stream leaves the heat regenerator HP-HT-HX2 throughthe flow passage 17 and enters the high-pressure combustor C₁ where itstemperature is further increased due to the combustion of the fuelstream 27. The resulting hot flue gas stream 37 enters the high-pressureturbine stage HPT where the high-pressure hot flue gas stream expands toa pressure slightly higher than the atmospheric pressure, allowing theturbine rotors to harness the mechanical power. The expanded flue gasstream exits the high-pressure turbine stage HPT through the flowpassage 38 which directs the flue gas stream to pass through the thirdhigh-pressure air heat regenerator HP-HT-HX2, thereby enabling theregeneration of its heat content to the high-pressure air stream 16. Theflue gas stream, having rejected heat, leaves the third high-pressureair heat regenerator HP-HT-HX2 through the flow passage 39, whichdirects the flue gas stream to pass through the high-pressure fuelpreheater HP-FL-HX to preheat fuel and then through the water preheaterWAT-HX to preheat water. The flue gas stream, having preheated thewater, leaves the water preheater WAT-HX through the flow passage 42,which directs the flue gas stream to enter the second low-pressure airheat regenerator LP-HT-HX. Eventually, the flue gas stream loses itslow-temperature heat content in the second low-pressure fuel preheaterLP-FL-HX2 by entering the preheater through the flow passage 43 andexiting through the flow passage 44, thereby expelling itself to theatmosphere.

The low-pressure cycle continues when the low-pressure air stream 2 aenters the first low-pressure air heat regenerator LP-LT-HX, where theair stream is heated to a certain temperature by the flue gas that flowsfrom the flow passage 57 to the flow passage 58. Then the heated airstream enters the second low-pressure heat regenerator LP-HT-HX throughthe flow passage 3, where the air stream is further heated by the fluegas that flows from the flow passage 42 to the flow passage 43. Thelow-pressure air stream, now heated to the temperature which is requiredto operate the fuel cell, enters the cathode of the fuel cell SOFCthrough the flow passage 4. In the high-temperature electrolyte of thefuel cell SOFC, the reformed fuel/steam stream 52 and the oxygen in thelow-pressure compressed air stream 4 react electrochemically, and amajor portion of the fuel undergoes oxidation while the fuel cellproduces electricity. As a result, hot partially oxidized fuel exits theanode through the flow passage 53, while the hot compressed air withless oxygen exits the cathode through the flow passage 5. The twostreams 5 and 53 are mixed into a post-combustor FC-PC, where the fuelcompletes the oxidation reaction producing the hot flue gas stream 54.

The hot flue gas streams 54 flows through the second high-pressure airheat regenerator HP-HT-HX1 rejecting heat and thereby heating thehigh-pressure air stream 15. The flue gas stream leaves the regeneratorHP-HT-HX1 through the flow passage 55 and enters the low-pressureturbine stage LPT, where the flue gas stream expands to a lower pressureclose to the atmospheric pressure, allowing the turbine rotors toharness the mechanical power. As shown in FIG. 22 , both turbine stagesLPT and HPT can be mounted on the same shaft to drive a single generatorG, which converts the mechanical power feed of the two turbine stages toan electrical power output. It should be mentioned here that theworkings of the two cycles would not be significantly altered if the twoturbine stages were to drive two separate generators.

The expanded flue gas, now at a pressure slightly higher than theatmospheric pressure, leaves the low-pressure turbine stage LPT throughthe flow passage 56 which directs the flue gas stream to pass throughthe first high-pressure air heat regenerator HP-LT-HX where thehigh-pressure air stream 14 is regeneratively heated. The flue gasstream then enters the first low-pressure air heat regenerator LP-LT-HXthrough the flow passage 57 where much of the heat content of the fluegas stream is used up to regeneratively heat the low-pressure compressedair stream 2 a. The flue gas stream leaves the first low-pressure airregenerator LP-LT-HX through the flow passage 58, which directs the fluegas stream to pass through the first low-pressure fuel preheaterLP-FL-HX1 where the flue gas stream loses its low-temperature heatcontent to preheat the low-pressure fuel. Eventually, the flue gasstream expels itself to the atmosphere through the flue passage 59, thuscompleting the two-stage power cycle.

In accordance with all the PATMI power generating schemes presented thusfar, the compressors and pumps in this combined cycle are driven by theelectric motors 401, 402, and 403, which are in turn driven by theelectricity produced by the fuel cell SOFC, possibly with a battery bank100 to store electricity. The battery bank 100 accommodates theimbalance of the fuel cell electric power supply and the powerconsumption of the electric motors.

As FIG. 22 shows, there is a somewhat open feature in this power cycle,which is in reference to the high-pressure water stream 33 b (denoted byA). There are a few options one could find to use the high-pressurewater stream 33 b to optimize the performance of this combined powercycle. The first method is to use the high-pressure water stream to coolthe high-temperature blades in the high-pressure turbine stage HPT (seeflow paths 34 denoted by D). The steam generated in this manner can befed into the low-pressure turbine stage LPT as described in reference toIllustrative Embodiment 18, thus increasing the power output of thecombined-cycle. The second method is to use the steam generated (seeflow path 34) to drive a separate Rankine (steam) cycle turbine, inwhich case most of the water can be recovered using a condenser and berefed to the power cycle. The third method is to inject this preheatedwater to the combined cycle at the locations denoted by B and C. This isimportant if the flue gas streams 55 and/or 37 are extremely hot (sayabove 1200° C.), and cooling is needed before those streams enter therespective turbine stages.

Illustrative Embodiment 20—Two-Stage PATMI Power Generation Scheme witha Rankine Bottoming Cycle and a Pre-Reformer/Reformer where Bled-Steamfrom the Rankine Turbine is Used for Fuel Reformation

This Illustrative Embodiment differs from Illustrative Embodiments thusfar described since this Illustrative Embodiment uses the bled steamfrom a Rankine steam cycle to reform the fuel prior to entering the fuelcell. Further, the Rankine cycle is partly driven by the regenerativeheat harnessed in the high-temperature blade cooling of thehigh-pressure gas turbine. The workings of this Illustrative Embodimentshown in FIG. 23 , can be described as follows. The description firstfocuses on the gaseous fuel supply circuits and the Rankine cycle, whichsupplies the bled-steam for reformation of fuel.

The two-stage fuel compressor, which is driven by an electric motor 402,comprises a low-pressure compression stage 20 a and a high-pressurecompression stage 20 b. The low-pressure compressor stage 20 a extractsthe gaseous fuel from the fuel supply line 21 and compresses the gaseousfuel to the low-pressure fuel delivery line 22. A portion of thiscompressed fuel is delivered to the low-pressure power cycle through theflow passage 23, while the remainder is further compressed by thehigh-pressure fuel compressor stage 20 b and is delivered to thehigh-pressure fuel delivery line 26. The high-pressure fuel deliveryline 26 passes through the high-pressure fuel preheater FL-HX3 and thenflows through the flow passage 27 to enter the high-pressure combustorC₁ where the fuel is mixed and combusted with the high-pressurecompressed air stream that enters through the flow passage 16.

The low-pressure fuel line 23 passes through the first low-pressure fuelpreheater FL-HX1, and so heated fuel is delivered to the secondlow-pressure fuel preheater FL-HX2 through the fuel flow passage 24. Theheated fuel stream leaves the second fuel preheater FL-HX2 through theflow passage 25 and enters the fuel/steam mixer M where the fuel streamis mixed with the high-pressure steam fed through the steam line 35. Themixed stream 28 enters the reformer/pre-reformer REF, where thefuel/steam mixture undergoes the reformation reaction producing asignificant amount of hydrogen. Since the reformation reaction isendothermic, the required heat for the reaction may be provided to thereformer REF by the recirculating the anode outlet stream 29 through theoptional recirculation path 29 a. The partially reformed fuel enters thefuel cell anode through the flow passage 28 a.

In this Illustrative Embodiment, the steam feed used in the reformationprocess is obtained from the Rankine steam cycle shown in FIG. 23 . Theassociated Rankine steam cycle can be described as follows. The waterpump 30 extracts the condensate from the Rankine cycle condenser CONDand pumps the water to the high-pressure water delivery line 32. Thehigh-pressure water stream 32 passes through the regenerative heatexchanger RK-HX, which acts as a water preheater/boiler. In the heatexchanger RK-HX the water stream 32 is partially vaporized by the heatharnessed from the flue gas stream, which flows from the flow passage 18to the flow passage 19. The steam stream 33 is diverted (A) to passthrough the high-temperature blade cooling passages 33 a in thehigh-pressure gas turbine HPT, thereby further heating the water/steamstream 33, converting it to superheated steam (B). The superheated steam(B) enters the steam turbine ST where the steam progressively expandsthrough the turbine rotor blades to the condenser pressure, allowing theturbine rotors to harness mechanical power, which in turn drives theelectricity generator G₂. In a certain suitably chosen location based onthe pressure in the steam turbine, a portion of the steam is bled-outand diverted through the flow passage 35 to the steam/fuel mixer M to beused in the fuel reformer. The major portion of steam that completes theexpansion process in the steam turbine, leaves the turbine and entersthe condenser COND through the flow passage 34. In the condenser COND,steam condenses losing its latent-heat content, and the condensate soproduced, mixed with the makeup water feed 31 enters the water pump 30through the flow passage 36, thus completing the Rankine steam cycle.

The two-stage main cycles begin when the atmospheric air is extracted bythe two-stage compressor through the air supply line 1, and the air iscompressed in the first stage compressor LPC to a pressure slightlyhigher than the pressure at which the fuel cell SOFC operates. The firstcompressor stage LPC delivers the low-pressure compressed air to theflow passage 2. The compressed air stream 2 is then split into twostreams, the first of which is delivered to the flow passage 2 a to beused in the low-pressure cycle. The second split stream is cooledthrough the inter-cooler IC and delivered to the inlet flow passage 13of the high-pressure compressor stage HPC, where the air stream isfurther compressed to a much higher pressure to be used in thehigh-pressure cycle.

The high-pressure cycle continues when the high-pressure compressorstage HPC delivers air to the flow passage 14. The high-pressurecompressed air stream 14 enters the first high-pressure air heatregenerator HP-LT-HX where the compressed air stream is heated by thehot flue gas stream which flows in the counter-flow direction from theflow passage 8 to flow passage 9. The heated high-pressure air stream 15is further heated in the second high-pressure air heat regeneratorsHP-HT-HX from the heat regenerated from the flue gas stream, which flowsfrom the flow passage 6 to the flow passage 7. The heated high-pressureair stream leaves the second high-pressure heat regenerator HP-HT-HXthrough the flow passage 16 and enters the high-pressure combustor C₁where its temperature is further increased by the combustion of the fuelstream 27. The resulting hot flue gas stream 17 enters the high-pressureturbine stage HPT where the high-pressure hot flue gas stream expands toa pressure somewhat higher than the atmospheric pressure, allowing theturbine rotors to harness mechanical power. In this IllustrativeEmbodiment, the high-pressure turbine stage HPT can operate with aconsiderably high inlet temperature since the turbine stage HPT isequipped with the blade-cooling passages. Eventually, the expanded fluegas stream exits the high-pressure gas turbine stage HPT through theflow passage 18, which directs the flue gas stream to pass through thebottoming Rankine cycle thermal feed heat exchanger RK-HX, therebyenabling the flue gas stream to regenerate its high-temperature heatcontent to drive the Rankine steam cycle. The flue gas stream, havingrejected heat, leaves the bottoming cycle heat regenerator RK-HX throughthe flow passage 19, which directs the flue gas stream to pass throughthe high-pressure fuel preheater FL-HX3 to preheat fuel. The flue gasstream, having preheated the fuel, leaves the high-pressure fuelpreheater FL-HX3 through the flow passage 41, which directs the flue gasstream to enter the second low-pressure air heat regenerator LP-HT-HX.Eventually, the flue gas stream loses its low-temperature heat contentin the second low-pressure fuel preheater FL-HX2 by entering the fuelpreheater through the flow passage 42 and exiting the fuel preheaterthrough the flow passage 43, thereby expelling itself to the atmosphere.

The low-pressure gas turbine cycle continues when the low-pressure airstream 2 a enters the first low-pressure air heat regenerator LP-LT-HX,where the low-pressure air stream is heated to a certain temperature bythe flue gas that flows from the flow passage 9 to the flow passage 11.Then the heated air stream enters the second low-pressure air heatregenerator LP-HT-HX through the flow passage 3, where the air stream isfurther heated by the flue gas that flows from the flow passage 41 tothe flow passage 42. The low-pressure air stream, now heated to thetemperature which is required to operate the fuel cell, enters thecathode of the fuel cell SOFC through the flow passage 4. In thehigh-temperature electrolyte of the fuel cell SOFC the reformedfuel/steam stream 28 a and the oxygen in the low-pressure compressed airstream 4 react electrochemically, and a major portion of the fuelundergoes oxidation while the fuel cell produces electricity. As aresult, hot partially oxidized fuel exits the anode through the flowpassage 29, while the hot compressed air with less oxygen exits thecathode through the flow passage 5. The two streams 5 and 29 are mixedinto a post-combustor FC-PC, where the fuel completes the oxidationreaction producing the hot flue gas stream 6.

The hot flue gas streams 6 flows through the second high-pressure airheat regenerator HP-HT-HX rejecting heat and thereby heating thehigh-pressure air stream 15. The flue gas stream leaves the regeneratorHP-HT-HX through the flow passage 7 and enters the low-pressure turbinestage LPT where the flue gas stream expands to a lower pressure close tothe atmospheric pressure, allowing the turbine rotors to harness themechanical power. As shown in FIG. 23 , both turbine stages LPT and HPTcan be mounted on the same shaft to drive a single generator G₁, whichconverts the mechanical power feed of the two turbine stages to anelectrical power output. It should be mentioned here that the workingsof the two cycles would not be significantly altered if the two turbinestages were to drive two separate generators.

The expanded flue gas, now at a pressure slightly higher than theatmospheric pressure, leaves the low-pressure turbine stage LPT throughthe flow passage 8 which directs the flue gas stream to pass through thefirst high-pressure air heat regenerator HP-LT-HX where thehigh-pressure air stream 14 is regeneratively heated. The flue gasstream then enters the first low-pressure air heat regenerator LP-LT-HXthrough the flow passage 9 where much of the heat content of the fluegas stream is used up to regeneratively heat the low-pressure compressedair stream 2 a. The flue gas stream leaves the first low-pressure airregenerator LP-LT-HX through the flow passage 11, which directs the fluegas stream to pass through the first low-pressure fuel preheater FL-HX1where the flue gas stream loses its low-temperature heat content topreheat the low-pressure fuel. Eventually, the flue gas stream expelsitself to the atmosphere through the flue passage 12, thus completingthe two-stage power cycle.

In accordance with all the PATMI power generating schemes presented thusfar, the compressors and pumps in this combined cycle are driven by theelectric motors 401, 402, and 403, which are in turn driven by theelectricity produced by the fuel cell SOFC, possibly with a battery bank100 to store electricity. The battery bank 100 accommodates theimbalance of the fuel cell electric power supply and the powerconsumption of the electric motors.

One noteworthy aspect of this combined-cycle is that the highestpressure in the Rankine steam cycle, which is the pressure of thehigh-pressure water delivery line, should be higher than the fuel celloperating pressure. It is a necessary condition for steam to be bledfrom the steam turbine and be used in the reformer of the fuel cell.

Illustrative Embodiment 21—Two-Stage PATMI Power Generation Scheme witha Fuel Cell Located Downstream of the High-Pressure Gas Turbine andSteam Recirculation is Assisted by an Ejector

This Illustrative Embodiment differs from the Illustrative Embodimentsdescribed thus far since this Illustrative Embodiment has its fuel cellplaced in the down-stream of the high-pressure turbine stage. ThisIllustrative Embodiment also contains an ejector/mixer device torecirculate the fuel cell anode outlet stream to apre-reformer/reformer. Another noteworthy feature here is that there isno high-pressure fuel circuit because there is no high-pressurecombustor in the power scheme. The workings of the IllustrativeEmbodiment can be described as follows in reference to FIG. 24 .

The two-stage main cycles begin when the low-pressure compression stageLPC extracts atmospheric air through the air supply line 1 andcompresses air to a pressure slightly higher than the pressure at whichthe fuel cell SOFC operates. The first compressor stage LPC delivers thelow-pressure compressed air to the flow passage 2, which is then splitinto two streams. The first of these split streams is delivered to theflow passage 2 a to be used in the low-pressure cycle, and the secondsplit stream is cooled through the inter-cooler IC and delivered to theinlet flow passage 13 of the high-pressure compressor stage HPC, wherethe second air stream is further compressed to a much higher pressure tobe used in the high-pressure cycle.

The high-pressure cycle continues when the high-pressure compressorstage HPC delivers air to the flow passage 14. The high-pressurecompressed air stream 14 enters the first high-pressure air heatregenerator HP-LT-HX where the compressed air stream is heated by thehot flue gas stream which flows in the counter-flow direction from theflow passage 31 to flow passage 32. The heated high-pressure air stream15 is further heated in the second high-pressure air heat regeneratorsHP-HT-HX from the heat regenerated from the flue gas stream 27 emittedby the post combustor FC-PC of the fuel cell SOFC, which flows throughthe regenerator to the flow passage 28. The heated high-pressure airstream leaves the second high-pressure heat regenerator HP-HT-HX throughthe flow passage 16 and enters the high-pressure turbine stage HPT,where the high-pressure hot flue gas stream expands to the fuel celloperating pressure, allowing the turbine rotors to harness mechanicalpower. The partially expanded air stream, now at the operating pressureof the fuel cell, leaves the high-pressure turbine stage HPT through theflow passage 17.

The single-stage fuel compressor 20, which is driven by an electricmotor 402, extracts the gaseous fuel from the fuel supply line 21,compresses the gaseous fuel to a pressure somewhat higher than theoperating pressure of the fuel cell, and delivers it to the main fuelfeed line 22. A portion of this compressed fuel branches off from themain fuel feed line 22 to the auxiliary fuel feed line 22 a and entersthe low-pressure combustor C₁, while the remainder of the main fuel feed22 enters the primary port of the ejector/mixer device EJC-M. Theejector device EJC-M, which acts as a pump, pulls a portion of the anodeoutlet flue-gas stream 26 through the ejector secondary stream 26 a,mixes it with the primary stream 22 inside the ejector, and the mixedstream is delivered to the reformer/pre-reformer REF through the flowpassage 24. The objective here is to pull enough flue gas, whichcontains water vapor and heat, to mix with the primary fuel feed so thatthe reformation reaction could begin in the pre-reformer/reformer.Eventually the partially reformed fuel enters the fuel cell anodethrough the flow passage 25.

The low-pressure gas turbine cycle begins when the low-pressure airstream 2 a enters the first low-pressure air heat regenerator LP-LT-HX,where the low-pressure air stream is heated to a certain temperature bythe flue gas that flows from the flow passage 29 to the flow passage 31.Then a portion of the heated air stream 3 enters the low-pressurecombustor C₁ where the pressurized auxiliary fuel stream 22 a iscombusted to generate the high-temperature flue gas stream 4, while theremainder of the heated air stream 3 branches off through the flowpassage 3 a to be further heated in the second low-pressure air heatregenerator LP-HT-HX. The branched-off air stream 3 a is heated using afraction of the heat content of the hot flue gas stream 4, which isexpelled from the combustor C₁. The flue gas stream 4, having rejected aportion of its heat, leaves the LP-HT-HX regenerator through the flowpassage 5, while the heated low-pressure air stream leaves theregenerator through the flow passage 4 a.

One important design feature to highlight here is that the use of theoptional heated air stream 4 a, generated by heating the air stream 3 a;the objective being to get sufficient heat to the fuel cell in case thestream 17 does not have the required temperature to operate thehigh-temperature SOFC fuel cell.

The heated hot air stream 4 a mixed with the hot air stream 17 whichexits the high-pressure turbine stage HPT, enters the cathode of thefuel cell SOFC. In the high-temperature electrolyte of the fuel cellSOFC, the reformed fuel/steam stream 25 and the oxygen in thelow-pressure compressed air stream 17 (which is now mixed with the airstream 4 a) react electrochemically, and a major portion of the fuelundergoes oxidation while the fuel cell produces electricity. As aresult, hot partially oxidized fuel exits the anode through the flowpassage 26, while the hot compressed air with less oxygen exits thecathode through the flow passage 18. The two outlet streams of the fuelcell 18 and 26 are mixed into a post-combustor FC-PC, where the fuelcompletes the oxidation reaction producing the hot flue gas stream 27.

The hot flue gas streams 27 flows through the second high-pressure airheat regenerator HP-HT-HX rejecting heat and thereby heating thehigh-pressure air stream 15. The flue gas stream leaves the regeneratorHP-HT-HX through the flow passage 28, which is then mixed with the hotflue gas stream 5, and the combined flue gas streams enter thelow-pressure turbine stage LPT. In the low-pressure turbine stage, theflue gas stream expands to a lower pressure close to the atmosphericpressure, allowing the turbine rotors to harness the mechanical power.As shown in FIG. 24 , both turbine stages LPT and HPT can be mounted onthe same shaft to drive a single generator G, which converts themechanical power output of the two turbine stages to an electrical poweroutput. It should be mentioned here that the workings of the two cycleswould not be significantly altered, but may provide some designflexibility, if the two turbine stages were to drive two separategenerators.

The expanded flue gas, now at a pressure slightly higher than theatmospheric pressure, leaves the low-pressure turbine stage LPT throughthe flow passage 29 which directs the flue gas stream to pass throughthe first low-pressure air heat regenerator LP-LT-HX where thelow-pressure air stream 2 a is regeneratively heated. The flue gasstream then enters the first high-pressure air heat regenerator HP-LT-HXthrough the flow passage 31 where much of the heat content of the fluegas stream is used up to regeneratively heat the high-pressurecompressed air stream 14. Eventually, the flue gas stream leaves thefirst high-pressure air regenerator HP-LT-HX through the flow passage32, and expels itself to the atmosphere, thus completing the two-stagepower cycle.

In accordance with all the PATMI power generating schemes presented thusfar, the air and fuel compressors in this combined cycle are driven bythe electric motors 401 and 402, which are in turn driven by theelectricity produced by the fuel cell SOFC, possibly with a battery bank100 to store electricity. The battery bank 100 accommodates theimbalance of the fuel cell electric power supply and the powerconsumption of the electric motors.

Illustrative Embodiment 22—Two-Stage PATMI Power Generation Scheme witha Reformer and an Advanced Rankine Bottoming Cycle Having SteamReheating

This Illustrative Embodiment consists of a two-stage gas turbine cycleand an advanced Rankine bottoming cycle. The two-stage gas turbine cycleoperates very similar to the Illustrative Embodiment 16 as it comprisesa gaseous fuel feed, a water/steam feed, and a reformer/pre-reformer. Inthis Illustrative Embodiment, the gaseous fuel is fed through two flowcircuits which operate at two pressure levels; the first of which is alow-pressure fuel feed to drive the low-pressure power cycle, that alsoincludes the fuel cell. The second is a high-pressure fuel feed to powerthe high-pressure power cycle. The workings of thisgas-turbine/steam-turbine combined cycle can be described as followswith reference to FIG. 25 . Since this Illustrative Embodiment has twoauxiliary flow layouts for a gaseous fuel (such as natural gas) feed anda water/steam feed, the description begins by emphasizing the operationof the two auxiliary layouts, prior to presenting the descriptions ofthe main two-stage gas-turbine cycle and the advanced Rankine cycle.

The electric motor 403 drives a water pump 30 which pumps atmosphericwater extracted from the water supply line 31 to the high-pressure waterdelivery line 32. The high-pressure water flows through the waterpreheater/boiler heat exchanger HX₆ where the water is converted tohigh-pressure steam. The generated steam is fed through the flow line 33(see location A) to a fuel/steam mixer M where the high-pressure steamis mixed with a gaseous high-pressure fuel.

The two-stage fuel compressor, which is driven by an electric motor 402,comprises a low-pressure compression stage 20 a and a high-pressurecompression stage 20 b. The low-pressure compressor stage 20 a extractsthe gaseous fuel from the fuel supply line 21 and compresses the fuel tothe low-pressure fuel delivery line 22. A portion of this compressedfuel is delivered to the low-pressure power cycle through the flowpassage 23, while the remainder is further compressed by thehigh-pressure compressor stage 20 b and is delivered to thehigh-pressure fuel delivery line 26. The high-pressure fuel deliveryline 26 passes through the first high-pressure fuel preheater HX₄ andthen flows through the flow passage 27 to enter the second high-pressurefuel preheater HX₁ where the high-pressure fuel stream is further heatedbefore the fuel stream enters the high-pressure combustor C₁ through theflow passage 28.

The low-pressure fuel line 23 passes through the first low-pressure fuelpreheater HX₅, and so heated fuel is delivered to the secondlow-pressure fuel preheater HX₂ through the fuel flow passage 24. Theheated fuel stream leaves the second fuel reheater HX₂ through the flowpassage 25, which is then split into two streams 25 a and 25 b. The fuelstream 25 b enters the low-pressure combustor C₂, while the other fuelstream 25 a enters the fuel/steam mixer M where the fuel stream is mixedwith the high-pressure steam fed through the steam line 33. The mixedstream 35 enters the reformer REF, where the fuel/steam mixtureundergoes the reformation reaction producing a significant amount ofhydrogen. Since the reformation reaction is endothermic, the requiredheat of the reaction may be provided to the reformer REF by partiallyrecirculating the anode output stream 37 through the optionalrecirculation path 35 a. The partially reformed fuel enters the fuelcell anode through the flow passage 36.

The two-stage gas-turbine cycle begins when the atmospheric air isextracted by the two-stage compressor through the air supply line 1, andthe air is compressed in the first-stage low-pressure compressor LPC toa pressure slightly higher than the fuel cell SOFC operating pressure.The first compressor stage LPC delivers the low-pressure compressed airto the flow passage 2. The low-pressure compressed air stream 2 is thensplit into two streams, the first of which is delivered to the flowpassage 2 a to be used in the low-pressure gas-turbine cycle. The secondsplit stream is cooled through the inter-cooler IC and delivered to theinlet flow passage 13 of the high-pressure compressor stage HPC, wherethe air stream is further compressed to a much higher pressure to beused in the high-pressure gas-turbine cycle.

The high-pressure gas-turbine cycle continues when the high-pressurecompressor stage HPC delivers air to the flow passage 14. Thehigh-pressure compressed air stream 14 enters the high-pressureregenerator REG where the compressed air stream is heated by the hotflue gas stream which flows in the counter-flow direction from the flowpassage 45 to flow passage 46. The heated air stream 15 enters thehigh-pressure combustor C₁ where its temperature is further increased bythe combustion of the fuel stream 28. The resulting extremely hot fluegas stream 16 enters the high-pressure turbine stage HPT where thehigh-pressure hot flue gas stream expands to a pressure slightly higherthan the inlet pressure of the low-pressure turbine LPT, allowing theturbine rotors to harness mechanical power. The expanded flue gas streamexits the high-pressure turbine stage HPT through the flow passage 17,which directs the flue gas stream to mix with the flow stream 39 andenter the low-pressure gas turbine stage LPT.

The low-pressure gas-turbine cycle continues when the low-pressure airstream 2 a enters the first low-pressure air preheater HX₃ where the airis heated to a certain temperature. The preheated low-pressure airstream leaves the first low-pressure air preheater through the flowpassage 3 which is then split into two streams 3 a and 3 b. The firstsplit low-pressure air stream 3 a enters the cathode of the fuel cellSOFC to power the fuel cell, while the second split low-pressure airstream 3 b enters low-pressure combustor C₂ where the fuel fed throughthe fuel line 25 b undergoes the combustion reaction to form a hot fluegas stream 4 b.

In the high-temperature electrolyte of the fuel cell SOFC, the gaseousfuel that enters through the flow passage 36 and the oxygen in thelow-pressure compressed air stream 3 a react electrochemically, and amajor portion of the fuel undergoes oxidation while the fuel cellproduces electricity. As a result, hot partially oxidized fuel exits theanode through the flow passage 37, while the hot compressed air withless oxygen exits the cathode through the flow passage 4 a. The twostreams 4 a and 37 are mixed into a post-combustor FC-PC, where the fueloxidation reaction comes to a completion. The resulting high-temperatureflue gas stream exits the post-combustor FC-PC through the flow passage38. The hot flue gas stream 38, which is combined with the flue gasstreams 17 and 4 b to form the mixed stream 39. The combined flue gasstream 39 enters the low-pressure turbine stage LPT where the combinedflue gas stream expands to a lower pressure close to the atmosphericpressure, allowing the turbine rotors to harness and deliver mechanicalpower. As shown in FIG. 25 both turbine stages can be mounted on thesame shaft to drive a single generator G₁, which converts the mechanicalpower feed of the two gas turbine stages to an electrical power output.It should be mentioned here that the workings of the two cycles will notbe significantly altered if the two turbine stages were to drive twoseparate generators.

The expanded flue gas, now at a pressure slightly higher than theatmospheric pressure, leaves the low-pressure turbine stage LPT throughthe flow passage 41. The flue gas stream 41 is then split into twoparallel streams 42 a and 42 b to form two parallel thermal feeds to thebottoming advanced Rankine cycle, the workings of which will bedescribed shortly. The returning flue gas lines 43 a and 43 b from theadvanced Rankine cycle thermal feed then are combined to form a singleflue gas stream 44, which is directed to pass through the secondhigh-pressure fuel preheater HX₁ to preheat the high-pressure fuelstream 28. The flue gas stream, having passed through the secondhigh-pressure fuel preheater HX₁, enters the high-pressure airregenerator REG through the flow passage 45 where much of the heatcontent of the flue gas stream is used up to regeneratively heat thehigh-pressure compressed air stream 14. The flue gas stream leaves thehigh-pressure air regenerator REG through the flow passage 46, whichdirects the flue gas stream to pass through the rest of the regenerativeheat exchanges: the second low-pressure fuel preheater HX₂; thelow-pressure air preheater HX₃; the first high-pressure fuel preheaterHX₄; the first low-pressure fuel preheater HX₅; and the water boilerHX₆, in that sequence, directed by the flow passages 46, 47, 48, 49, and51 respectively. Eventually, the flue gas stream expels itself to theatmosphere through the flue passage 52, thus completing the two-stagegas-turbine power cycle.

The bottoming advanced Rankine cycle shown in FIG. 25 has two steamturbine stages, in between which, the steam is reheated. There are foursteam bleeding locations in this power cycle. The first high-pressuresteam bleeding point is placed in the high-pressure turbine stage, andtwo more steam bleeding points are placed in the low-pressure turbinestage. The fourth steam bleeding point is placed at the inlet to thesteam reheater, which is placed in between the two turbine stages. Thefirst three high-pressure feed water heaters are of the closed types,while the last low-pressure feed water heater is an open type. Since thepressure of steam along the turbine progressively drops from turbineupstream to the turbine downstream, the feed water heaters operate atprogressively-reducing pressures corresponding to the bleeding points ofthe turbines.

The workings of the proposed advanced Rankine power scheme can bedescribed with reference to FIG. 25 as follows. The first-stage pump 60a extracts condensed water from the condenser COND through the watersuction line 61 and pumps the water to the open feed water heater OFWHthrough the water feedline 62. In the open feed water heater OFWH, thewater is heated to a certain degree by mixing it with the bled steam,which enters through the bleed line 74. The second-stage pump 60 bextracts water from the open feed water heater OFWH, through thesecond-stage pump suction line 63 and pumps through the three closedfeed water heaters CFWH1, CFWH2, and CFWH3, through the flowlines 64,65, and 66 respectively. In the three closed feed water heaters, thewater is progressively heated regeneratively by the heat harnessed fromthe bled-steam streams 71, 72, and 73, which reject their latent heatand the steam condenses inside the closed feed water heaters. Thecondensed water inside each closed feed water heater flashes throughtheir individual throttle valve into the adjacent low-pressure feedwater heater. Thus, the condensed water in the feed water heater CFWH3flashes through the throttle valve 73 a into the feed water heater CFWH2and condenses in CFWH2 further rejecting heat; the condensed water inthe feed water heater CFWH2 flashes through the throttle valve 72 a intothe feed water heater CFWH1 and condenses in CFWH1 further rejectingheat. The last step of the condensed water flashing occurs when thecondensed water in the closed feed water heater CFWH1 flashes throughthe throttle valve 71 a into the open feed water heater OFWH where thecondensate is mixed with the main water feed 63. Eventually, the heatedfeed water stream 67 enters the boiler/superheater BO-SH where water isvaporized and steam is generated by the heat rejected from the firstthermal feed (flue gas feed from 42 a to 43 a) of the gas-turbine cycle.The generated steam enters the high-pressure steam turbine stage HPSTand expands allowing the turbine rotors to harness mechanical power.During the expansion process that occurs in HPST, a minute amount ofsteam is bled through the bleed line 73 and is fed to the closed feedwater heater CFWH3. The remainder of the steam expands in thehigh-pressure turbine stage HPST and is directed to the reheater REHthrough the flow passage 69. At the steam inlet of the reheater REH,another minute amount of steam is bled through the bleed line 72 and isfed to the closed feed water heater CFWH2. The remainder of the steamflows through the steam reheater feedline 69 and enters the reheater REHto be heated by the second thermal feed (flue gas feed from 42 b to 43b) of the gas-turbine cycle. The reheated steam leaves the reheaterthrough the flow passage 75 and enters the low-pressure steam turbinestage LPST, where the steam expands further allowing the turbine rotorsto harness mechanical power.

As shown in FIG. 25 , the two steam turbine stages HPST and LPST can bemounted on the same shaft to drive a single generator G₂, in order toachieve some design flexibility. The steam that expands in thelow-pressure steam turbine stage LPST is bled at two bleed locations.The first is bled through the bleed line 71 and is fed to the closedfeed water heater CFWH1, and the second is bled through the bleed line74 and is fed to the open feed water heater OFWH. Eventually, the steamexpands in the low-pressure steam turbine stage LPST until its pressureequals the condenser pressure, exits the turbine, and enters thecondenser through the flow passage 76. In the condenser, steam condensesrejecting its latent heat forming the condensate, thus completing theadvanced Rankine cycle.

One noteworthy aspect of this combined cycle power scheme is that, asshown in FIG. 25 , blade cooling can be incorporated (shown as the openflow path C to D in FIG. 25 ) in the high-pressure gas turbine stage,thereby increasing the inlet temperature of the high-pressure gasturbine stage. This design feature gives an added advantage as thisthermal feed could be used to supplement one of the thermal feeds of thebottoming Rankine cycle, thereby enhancing the performance of thecombined cycle.

In accordance with all the PATMI power generating schemes presented thusfar, all compressors and pumps in this combined cycle, including thepumps in the advanced Rankine cycle, are driven by the electric motors401, 402, 403, and 404, which are in turn driven by the electricityproduced by the fuel cell SOFC, possibly with a battery bank 100 tostore electricity. The battery bank 100 accommodates the imbalance ofthe fuel cell electric power supply and the power consumption of theelectric motors.

Illustrative Embodiment 23—Three-Stage PATMI Power Generation Schemewith Two-Series Brayton/sCO₂ Bottoming Cycles

This Illustrative Embodiment is very similar to the IllustrativeEmbodiment 13 described previously; however, this IllustrativeEmbodiment is a triple-combined cycle, which comprises of threeindependent cycles in cascade, forming two sets oftopping-bottoming-cycle pairs. The top-most cycle (the primary cycle) isa fuel cell integrated gas-turbine plant, which resembles theIllustrative Embodiment 13. Its bottoming-cycle (the secondary cycle) isan independent Brayton cycle, which is partly powered by the heatrejected by the primary cycle. The second bottoming-cycle (the tertiarycycle) is a split-flow recompression supercritical carbon dioxide (sCO₂)cycle which is fully driven by a thermal feed from the secondary cycle.

The workings of the triple-combined cycle can be described as follows inreference to FIG. 26 . The primary cycle begins when the compressor C₁extracts atmospheric air from its intake line 1 and compresses air to apressure just above the operating pressure of the fuel cell FC. Thecompressor C₁ delivers the compressed air stream, now at a temperaturesomewhat higher than the ambient temperature, to the flow passage 2. Theair stream 2 then enters the low-temperature heat exchanger LT-HX to beheated by the regenerated heat. As shown in FIG. 26 , the compressed airstream 2 is heated regeneratively as it passes through the twocounter-flow heat exchangers LT-HX and HT-HX, which are placed inseries. The compressed air stream 2 is first heated as it passes throughthe low-temperature first-stage heat exchanger LT-HX by the relativelycooler flue gas stream which flows from the flow passage 10 to the flowpassage 11. The heated compressed air stream exits the heat exchangerthrough the flow passage 3. The compressed air stream 3 is then splitinto two streams, one of which flows through the by-pass flow passage 4,and the other stream 3 a is further heated as it passes through thehigh-temperature second-stage heat exchanger HT-HX by the relativelyhotter flue gas stream which flows from the flow passage 9 to the flowpassage 10. The heated compressed air stream is fed to the cathode ofthe fuel cell FC through the flow passage 5. The fuel, in this case hotsyngas, generated from an incineration process and subsequently filteredto remove all undesirable constituents, is fed to the anode of the fuelcell FC through the flow passage A.

In the high-temperature electrolyte of the fuel cell FC, the gaseousfuel and the oxygen in the compressed air stream 5 reactelectrochemically, and a portion of the fuel undergoes oxidation whilethe fuel cell produces electricity. As a result, hot partially oxidizedfuel exits the anode through the flow passage D, while the hotcompressed air with less oxygen exits the cathode through the flowpassage E. The two streams D and E are mixed into a post-combustor PC,where the fuel is allowed to complete the oxidation reaction. Theresulting high-temperature flue gas stream exits the post-combustor PCthrough the flow passage 7. As mentioned with reference to theIllustrative Embodiment 10, the temperature of the stream 7 depends onthe fuel utilization factor of the fuel cell FC.

The bypassed compressed air stream 4 is directed through an auxiliarycombustor AC to increase its temperature to a desired value andconsequently exits through the flow passage 4 a. The hot flue gas mixedstream 7 and the heated by-pass compressed air stream 4 a are thencombined and mixed in a static mixing device M₁ to form a mixed hot fluegas stream 8 a. The flue gas stream 8 a is then fed to the heatexchanger PRI-SEC-HX to harness a portion of its heat content to thesecondary power cycle. The stream 8 a, having been cooled in the heatexchanger PRI-SEC-HX to a certain degree, leaves the heat exchangerthrough the flow passage 8. The flue gas stream 8 enters the turbine T₁,where the stream expands to a lower pressure close to the atmosphericpressure allowing the turbine rotors to harness the mechanical power.The power harnessed by the turbine rotors drives the electric generatorG₁, which converts the mechanical power output of the turbine toelectricity. Eventually, the flue gas, now at a pressure very close tothe atmospheric pressure, leaves the turbine through the flow passage 9,and the stream passes through the heat exchangers HT-HX and LT-HX, inthat sequence, passing through the flow passages 10 and 11 toregeneratively heat the counter-flow compressed air stream 2 to producethe hot air stream 5. The primary power cycle completes when theflue-gas stream expels itself to the atmosphere through the flow passage11.

The secondary Brayton cycle begins when the Low-pressure, firstcompression stage BC₁ extracts atmospheric air through the air-intakeB1. The first compression stage raises the pressure of the air to acertain level and delivers to the first inter-cooler stage IC-1. Havingcooled in the first inter-cooler stage IC-1, the partially compressedair then enters the second stage compressor BC₂. In this manner the airis progressively compressed while it is cooled in the inter-coolerstages IC-2 and IC-3 between the compression stages BC₂ and BC₃. Thecompression process is completed when the air stream is compressed inthe last compression stage BC₄, after passing through the inter-coolerIC-3 and enters the flow passage B2. The flow passage B2 directs thecompressed air stream to the first regenerative heat exchanger BC-HX. Inthe heat exchanger BC-HX, the air stream is heated by the hot flue gasstream which enters from the flow passage B7 and flows in thecounter-flow direction rejecting heat. The compressed air stream leavesthe heat exchanger BC-HX through the flow passage B3, with itstemperature being raised to a certain high temperature. The flow passageB3 directs the compressed air stream to the topping-cycle heatregenerator PRI-SEC-HX where the secondary cycle air stream is furtherheated with the heat rejected by the primary cycle flue gas stream,which flows from the flow passage 8 a to the flow passage 8.

Having heated the compressed air stream in the heat exchangerPRI-SEC-HX, the air stream flows into the fuel combustor BAC, where thecompressed air stream is further heated by combusting a suitable fuel inthe air stream. The combustion of fuel in the air stream converts thecompressed air stream B4 to a hot flue gas stream B5, which exits thecombustor at the highest temperature of the secondary cycle and entersthe secondary cycle turbine BT. In the turbine BT the high-pressure,high-temperature flue gas stream expands, while the turbine rotorsharness the mechanical power from the expanding gas, enabling theturbine rotors to drive the electric generator G₂, thus producingelectricity. The expanded flue gas stream leaves the turbine BT throughthe flow passage B6 and enters the regenerative heat exchangerSEC-TER-HX, which provides the thermal feed to the supercriticalcarbon-dioxide tertiary cycle. In the heat exchanger SEC-TER-HX, theflue gas stream decreases its temperature by rejecting heat, and socooled flue gas stream leaves the heat exchanger SEC-TER-HX through theflow passage B7 and enters the first regenerative heat exchanger BC-HXto provide heat to the compressed air stream B2 as described earlier.Eventually, the flue gas stream leaves the heat exchanger BC-HX throughthe flow passage B8 and expels itself to the atmosphere completing thesecondary cycle.

The tertiary cycle is a split-flow recompression sCO₂ cycle operates asdescribed under the Illustrative Embodiment 9(b). The tertiary cycleshown in FIG. 26 gets its sole thermal feed from the secondary cyclefrom the SEC-TER-HX heat exchanger.

In accordance with all the PATMI power generating schemes presented thusfar, the compressors in this triple-combined cycle are driven by theelectric motors 401, 402, and 403; they are in turn driven by theelectricity produced by the fuel cell FC in the primary cycle, possiblywith a battery bank 100 to store electricity. The battery bank 100accommodates the imbalance of the fuel cell electric power supply andthe power consumption of the electric motors.

There are several noteworthy points in this Illustrative Embodiment. Thefirst point is that the pressure ratio of the primary cycle isdetermined by the fuel cell operation pressure. Since high-pressure SOFCfuel cells work in the range 350-400 kPa, the typical pressure ratiorange of the primary cycle is 3.5-4.5. The second noteworthy point isthat the pressure ratio of the secondary cycle turbine needs to bedetermined in relation to two factors; the first factor is thetemperature of the turbine input stream B5. The second factor is thetemperature of the stream C7 of the tertiary cycle. Typically, thetertiary sCO₂ cycle to perform optimally, its maximum temperature, whichis at the turbine inlet, should be around 650-700° C.

In the disclosure, the phrases “near-atmospheric pressure” and“near-fuel cell operating pressure” are commonly used in the followingcontext. The pressure drops across expanders are very significant. In atypical turbine expander, the pressure drop is such that the ratiobetween inlet to outlet pressure will be in 2-10 range. However, thepressure drops in many heat exchanges are not that significant. Typicalwell-designed heat-exchanger flow passages have pressure drops in therange 3-10% of the inlet pressure depending on the number ofheat-exchanger flow passages that are placed in series.

Therefore, in the instances where a gas expands in an expander andpasses through a number of heat exchanger passages before the gas isexpelled to the atmosphere, the phrase “the gas expands tonear-atmospheric pressure” is used in some embodiments to mean that atthe outlet of the expander, the gas pressure is 3-10% higher than theatmospheric pressure to allow the pressure drop across theheat-exchangers in the downstream of the expander.

Similarly, in the instances where a gas expands in an expander andpasses through a number of heat exchanger passages before the gas entersa fuel cell or the gas is mixed with the another gaseous stream expelledby a fuel cell, the phrase “the gas expands to near-operating pressureof the fuel cell” is used in some embodiments to mean that at the outletof the expander, the gas pressure is 3-10% higher than the fuel celloperating pressure to allow the pressure drop across the heat-exchangerflow passages.

It should be highlighted that any of the features or attributes of theabove described embodiments and variations can be used in combinationwith any of the other features and attributes of the above describedembodiments and variations as desired.

Although the invention has been shown and described with respect to acertain embodiment or embodiments, it is apparent that this inventioncan be embodied in many different forms and that many othermodifications and variations are possible without departing from thespirit and scope of this invention.

Moreover, while exemplary embodiments have been described herein, one ofordinary skill in the art will readily appreciate that the exemplaryembodiments set forth above are merely illustrative in nature and shouldnot be construed as to limit the claims in any manner. Rather, the scopeof the invention is defined only by the appended claims and theirequivalents, and not, by the preceding description.

The invention claimed is:
 1. A power generation system, comprising: afirst subsystem, the first subsystem including one or more mechanicalwork-consuming components, and the one or more mechanical work-consumingcomponents including at least one compressor or one pump; a secondsubsystem, the second subsystem including one or more components thatoutput mechanical work, and the one or more components that outputmechanical work including at least one expander; a third subsystem, thethird subsystem including one or more heat-consuming components, and theone or more heat-consuming components including at least one heatexchanger with an external thermal feed to the power generation system;and a fourth subsystem, the fourth subsystem including one or more heatsinks in the power generation system which dissipate heat to thesurroundings, the one or more heat sinks including a single heat sink orflue gas outlet; wherein the first, second, third, and fourth subsystemsare configured to interact with each other by exchanging matter from oneor more working fluids and by exchanging heat; and wherein, when thepower generation system is in operation for a particular finite timeperiod, the first subsystem consumes W_(in) quantity of mechanical workfrom one or more external sources, the third subsystem consumes Qquantity of heat from one or more external sources, while the secondsubsystem outputs W_(out) quantity of mechanical work, such that theenergy conversion efficiency of the power generation system is greaterthan (W_(out)−W_(in))/Q.
 2. The power generation system according toclaim 1, wherein the consumed mechanical work (W_(in)) by the firstsubsystem is supplied by a renewable energy source comprising windelectric generators, solar photovoltaic electricity generators, hydrogengas generators, and/or fuel cell electric generators; and the outputmechanical work (W_(out)) of the second subsystem is utilized to drive aload which consumes mechanical work.
 3. The power generation systemaccording to claim 2, wherein a portion of the consumed heat (Q) by thethird subsystem is supplied by external heat sources, the external heatsources including solar thermal collectors, geo-thermal sources, and/orany other renewable energy driven process in which heat is liberated asa byproduct.
 4. The power generation system according to claim 3,wherein the power generation system exchanges the one or more workingfluids with exterior surroundings, and the fourth subsystem dissipatesheat to the exterior surroundings by releasing the one or more workingfluids to the exterior surroundings, thus operating in an open cycle. 5.The power generation system according to claim 3, wherein the powergeneration system is sealed and enclosed from exterior surroundings sothat the one or more working fluids are not exchanged between the powergeneration system and the exterior surroundings; the at least one heatexchanger of the third subsystem being externally heated so as to heatthe enclosed one or more working fluids, thus providing a means ofsupplying heat to the power generation system; and the fourth subsystemcomprising at least one externally cooled heat exchanger so as to coolthe one or more working fluids and provide a means of dissipation ofheat from the power generation system, thus the power generation systemoperates in a closed cycle.
 6. The power generation system according toclaim 4, wherein the first subsystem comprises one or more compressorswhich extract atmospheric air, and the one or more compressors compressthe atmospheric air to pressures higher than atmospheric pressure; andthe at least one expander of the second subsystem comprises one or morerotary or reciprocating expanders configured to expand heated compressedair delivered by the third subsystem, thus forming a low-pressure powercycle.
 7. The power generation system according to claim 6, wherein aportion of the consumed heat (Q) in the third subsystem is suppliedinternally by combusting environmentally-friendly fuels in suitablydesigned combustion chambers.
 8. The power generation system accordingto claim 7, wherein the at least one heat exchanger of the thirdsubsystem comprises one or more heat regenerators to convey heat fromhigh-temperature flow passages of the power generation system tolow-temperature flow passages in the power generation system.
 9. Thepower generation system according to claim 8, wherein the firstsubsystem comprises a plurality of compressor stages which are fluidlycoupled in sequence through respective intercoolers, so that a primaryworking fluid stream is progressively compressed as the primary workingfluid stream flows through the plurality of compressor stages and iscooled as the primary working fluid stream passes through the respectiveintercoolers from an adjacent low-pressure compressor stage to asuccessive high-pressure compressor stage.
 10. The power generationsystem according to claim 9, wherein the consumed mechanical work(W_(in)) by the first subsystem is supplied by one or more fuel cellelectric generators and the waste heat liberated by the one or more fuelcell electric generators augment the heat supply to the third subsystem.11. The power generation system according to claim 10, wherein the atleast one expander of the second subsystem is an adiabatic expander. 12.The power generation system according to claim 10, wherein the fourthsubsystem includes a heat exchanger to discharge thermal energy to abottoming cycle which contains an additional power generation system asdescribed in claim 1; wherein the components of the combined cyclescollectively form a single set of subsystems defined in claim 1 as thefirst, the second, the third, and the fourth subsystems.
 13. The powergeneration system according to claim 11, wherein the fourth subsystemincludes a heat exchanger to discharge thermal energy to a bottomingcycle which contains an additional power generation system as describedin claim 1; wherein the components of the combined cycles collectivelyform a single set of subsystems defined in claim 1 as the first, thesecond, the third, and the fourth subsystems.
 14. The power generationsystem according to claim 5, wherein the fourth subsystem includes aheat exchanger to discharge thermal energy to a bottoming cycle whichcontains an additional power generation system as described in claim 1;wherein the components of the combined cycles collectively form a singleset of subsystems defined in claim 1 as the first, the second, thethird, and the fourth subsystems.
 15. The power generation systemaccording to claim 5, wherein the at least one heat exchanger of thethird subsystem is an externally-heated heat exchanger, and the thirdsubsystem further comprises a cold-side of at least one heatregenerator, so that the working fluid is heated independently as theworking fluid passes through the cold-side of the at least oneregenerator and also as the working fluid passes through the externalheat-exchanger; wherein the one or more heat sinks of the fourthsubsystem comprise at least one externally cooled heat-exchanger and thehot-side of the at least one regenerator in a series arrangement, sothat the working fluid is cooled first as the working fluid passesthrough the hot-side of the at least one regenerator and then as theworking fluid passes through the externally cooled heat-exchanger; andwherein the working fluid cycles through the first, second, third andfourth subsystems which are fluidly coupled to achieve a flow order fromthe first subsystem to the third subsystem, then to the secondsubsystem, then to the fourth subsystem, and finally back to the firstsubsystem, thus forming a closed-loop power cycle.
 16. The powergeneration system according to claim 15, wherein, in the thirdsubsystem, the cold-side of the at least one regenerator and theexternally-heated heat exchanger are in a series arrangement so that theworking fluid is heated first as the working fluid passes through thecold-side of the at least one regenerator, and then further heated asthe working fluid passes through the externally-heated heat exchanger.17. The power generation system according to claim 16, wherein the oneor more mechanical work-consuming components of the first subsysteminclude at least two compressor stages, between which an externallycooled intercooler that falls within the fourth subsystem is placed tocool the partially compressed working fluid between the compressorstages.
 18. The power generation system according to claim 17, whereinthe third subsystem is extended by including an externally-heatedlow-temperature heat exchanger between the inlet and the outlet pointsof the cold-side flow passages of the at least one heat regenerator,thus forming a parallel fluid stream to the cold-side flow passages ofthe at least one heat regenerator, so that the working fluid stream thatexits the first subsystem is divided into two parallel streams of whichthe first portion flows through the externally-heated low-temperatureheat exchanger, while the second portion of the working fluid flowsthrough the cold-side of the at least one heat regenerator.
 19. Thepower generation system according to claim 16, wherein the regenerationprocess occurs in at least two stages in series such that the at leastone regenerator comprises a low-temperature regenerator followed by ahigh-temperature regenerator; and wherein the cold-side flow passages ofthe low-temperature regenerator are fluidly coupled to the cold-sideflow passages of the high-temperature regenerator so that the workingfluid is heated as the working fluid passes through the cold-side of thelow-temperature regenerator first and then through the cold-side of thehigh-temperature regenerator, hence the cold-side flow passages of theregenerators form a part of the third subsystem.
 20. The powergeneration system according to claim 19, wherein the hot-side flowpassages of the two regenerator stages are fluidly coupled, so that theworking fluid is cooled as the working fluid passes through the hot-sideof the high-temperature regenerator first and then through the hot-sideof the low-temperature regenerator, hence the hot-side flow passages ofthe regenerators form a part of the fourth subsystem.
 21. The powergeneration system according to claim 20, wherein at least one additionalcompressor stage is included to the first subsystem to extract workingfluid from the inlet of the external cooling heat-exchanger, thenrecompress and feed to the fluid coupling which interconnects thecold-side flow passages of the two regenerators.
 22. The powergeneration system according to claim 19, wherein at least one additionalcompressor stage is included to the first subsystem, which is fluidlycoupled to the hot-sides of the low and high-temperature regenerators,so that the working fluid that flows out of the hot-side of thehigh-temperature regenerator is recompressed by the additionalcompressor to a higher pressure prior to entering the hot-side flowpassages of the low-temperature regenerator.
 23. The power generationsystem according to claim 21, wherein a second cooling heat-exchangerand a third compression stage are included in the flow passage thatconnects the hot-side outlet of the low-temperature regenerator to theinlet of the first cooling heat-exchanger, so that the working fluidthat exits the hot-side of the low-temperature regenerator is firstcooled and then compressed prior to entering the first cooling heatexchanger.
 24. The power generation system according to claim 15,wherein the power generation system comprises at least two heatregenerators in the form of a low-temperature regenerator and ahigh-temperature regenerator, whose cold-sides are fluidly coupled, sothat the working fluid is heated as the working fluid passes through thecold-side of the low-temperature regenerator first and then through thecold-side of the high-temperature regenerator, hence the cold-sides ofthe low-temperature and high-temperature regenerators form a part of thethird subsystem; and the hot-sides of the high and low-temperatureregenerators are fluidly coupled, so that the working fluid is cooled asthe working fluid passes through the hot-side of the high-temperatureregenerator first and then through the hot-side of the low-temperatureregenerator, hence the hot-sides of the high-temperature andlow-temperature regenerators form a part of the fourth subsystem;wherein the at least one expander of the second subsystem comprises afirst expander and a second expander, the inlet of the first expander isfluidly coupled to the outlet of the cold-side of the high-temperatureregenerator, so that the first expander is fed with the heated workingfluid from the cold-side of the high-temperature regenerator, the outletof the first expander is fluidly coupled to the inlet of the hot-side ofthe low-temperature regenerator; and wherein the inlet of the secondexpander is fluidly coupled to the outlet of the at least one compressorin the first subsystem through the externally-heated heat exchanger inthe third subsystem, so that a portion of the compressed working fluidfrom the first subsystem is diverted to the second expander through theexternally-heated heat exchanger, and the outlet of the second expanderis fluidly coupled to the inlet of the hot-side of the high-temperatureregenerator.
 25. The power generation system according to claim 15,wherein the power generation system comprises at least two regeneratorsin the form of a low-temperature regenerator and a high-temperatureregenerator, whose cold-sides are fluidly coupled, so that the workingfluid is heated as the working fluid passes through the cold-side of thelow-temperature regenerator first and then through the cold-side of thehigh-temperature regenerator, hence the cold-sides of thelow-temperature and high-temperature regenerators form a part of thethird subsystem; and the hot-sides of the high and low-temperatureregenerators are fluidly coupled, so that the working fluid is cooled asthe working fluid passes through the hot-side of the high-temperatureregenerator first and then through the hot-side of the low-temperatureregenerator, hence the hot-sides of the high-temperature andlow-temperature regenerators form a part of the fourth subsystem;wherein the at least one expander of the second subsystem comprises afirst expander and a second expander, the inlet of the first expander isfluidly coupled to the outlet of the cold-side of the high-temperatureregenerator, so that the first expander is fed with the heated workingfluid from the cold-side of the high-temperature regenerator, and theoutlet of the first expander is fluidly coupled to the inlet of thehot-side of the low-temperature regenerator; and wherein the inlet ofthe second expander inlet is fluidly coupled to the outlet of thecold-side of low-temperature regenerator through the externally-heatedheat exchanger in the third subsystem, so that a portion of thecompressed working fluid from the first subsystem is heated in thecold-side of the low-temperature regenerator and is diverted to thesecond expander through the externally-heated heat exchanger, and theoutlet of the second expander is fluidly coupled to the inlet of thehot-side of the high-temperature regenerator.
 26. The power generationsystem according to claim 10, wherein the fuel used in the combustionchambers and/or in fueling the fuel cell is a cold liquefied gas, theliquefied gas is fed to the power generation system by a pump and isgradually heated to the gaseous state through a series of heatexchangers; a first heat exchanger through which the liquefied gaspasses through is located in the intake of the first compressor stagewhich operates at the lowest pressure which will be heated by theatmospheric air intake; a second set of heat exchangers through whichthe liquefied gas passes through are the intercoolers located in betweenthe compressor stages; the liquefied gas is also heated by the heatliberated by the fuel cell; and the liquefied gas is also heated by thelast stage of a flue-gas stack after the internal or external heatregenerator.
 27. The power generation system according to claim 7,wherein the power generation system comprises a first set of one or morecompressors that form part of the first subsystem, a first set of one ormore expanders that form part of the second subsystem, cold-flowpassages of a first set of one or more heat regenerators that form partof the third subsystem where the working fluid gains heat, and hot-flowpassages of the first set of the one or more heat regenerators that formpart of the fourth subsystem where the working fluid rejects heat; andthe power generation system further comprises one or more fuel cellswhich operate at a fuel cell operating pressure, the one or more fuelcells generate direct current (DC) electricity to power electricalmotors to drive all the mechanical work-consuming components; whereinthe first set of one or more compressors extract atmospheric air,compress the atmospheric air to produce a compressed air stream, and theone or more compressors deliver the compressed air stream at a pressurejust above the fuel operating pressure of the one or more fuel cells.28. The power generation system according to claim 27, wherein the firstset of the one or more compressors delivers compressed air to thecold-flow passages of the first set of one or more heat regenerators sothat heated compressed air is fed to cathode flow passages of the one ormore fuel cells, while a compressed and heated gaseous fuel is fed toanode flow passages of the one or more fuel cells, the one or more fuelcells generating electricity by electrolytic oxidation reaction thattakes place in a fuel cell electrolyte layer at a high temperature,between a portion of the fuel fed to the anode flow passages and aportion of the oxygen in the compressed air stream fed to the cathodeflow passages; wherein the hot gas streams expelled by the anode andcathode flow passages are fed to a post-combustor where the unreactedfuel is allowed to complete its oxidation reaction by combining with theoxygen in the hot compressed air stream, the post combustor thusexpelling a hot flue gas stream comprising the combustion products;wherein the flue gas stream expelled by the post-combustor is fed to thefirst set of one or more expanders, the first set of one or moreexpanders producing mechanical power to drive one or more alternatingcurrent (AC) electricity generators, the flue gas expands in the one ormore expanders to near-atmospheric pressure; wherein the expanded fluegases expelled by the first set of one or more expanders passes throughthe hot-flow passages of the first set of heat regenerators in a seriesarrangement from the highest temperature regenerator to the lowesttemperature regenerator; and wherein the flue gas stream has rejectedheat now at approximately atmospheric pressure that escapes to theatmosphere, thus forming the low-pressure power cycle.
 29. The powergeneration system according to claim 28, wherein the first set of heatregenerators comprises two or more heat regenerators placed in series,so that the compressed air supplied by the first set of one or morecompressors flows through the lowest temperature heat regenerator to thehighest temperature heat regenerator in the sequence of progressivelyincreasing temperature; wherein a portion of the compressed air isextracted through a bypass flowline from a port placed in between thefirst set of heat regenerators so that the bypassed air stream is notfully heated as the non-bypassed stream that flows into the cathode flowpassages of the one or more fuel cells; wherein the partially heatedbypassed compressed air stream is mixed with the hot flue gas streamexpelled by the post combustor in a mixing chamber so as to form a mixedstream that is fed to the first set of one or more expanders, the firstset of expanders generating mechanical power to drive the one or morealternating current (AC) electricity generators; wherein the one or morefuel cells generate direct current (DC) electricity to drive the firstset of one or more compressors; and wherein the direct current (DC)electricity generated by the one or more fuel cells in excess of thepower consumed by the first set of one or more compressors in thelow-pressure power cycle is used to drive an additional alternatingcurrent (AC) electricity generator.
 30. The power generation systemaccording to claim 27, wherein the power generation system comprises asecond set of one or more compressors that form part of the firstsubsystem, a second set of one or more heat regenerators with coldpassages and hot passages that form parts of the third and fourthsubsystems respectively, a second set of one or more expanders that formpart of the second subsystem, and an intercooler device that belongs tothe fourth subsystem; wherein an air stream extracted from an outlet ofthe first set of compressors is externally cooled as the air streamflows through the intercooler, so the cooled air stream is furthercompressed to a higher pressure in the second set of one or morecompressors, so the compressed air stream is fed to the cold-passages ofthe second set of heat regenerators so that the air stream flows fromthe lowest temperature heat regenerator to the highest temperature heatregenerator in the sequence of progressively increasing temperature, sothat heated air is allowed to expand in the second set of one or moreexpanders, the expanded air stream then passes through the hot-passagesof the first and the second set of the heat regenerators from thehighest temperature heat regenerator to the lowest temperature heatregenerator in the sequence of progressively decreasing temperature,thus forming a high-pressure power cycle which is integrated to thelow-pressure power cycle; and wherein the direct current (DC)electricity generated by the one or more fuel cells drives the first andthe second sets of the one or more compressors.
 31. The power generationsystem according to claim 30, wherein the power generation systemcomprises a third set of heat regenerators, the high-pressure air streamheated by the second set of heat regenerators in the high-pressure cycleis further heated as the high-pressure air stream passes through thecold-passages of the third set of regenerators by low-pressure cycleflue gases passing through hot-passages of the third set ofregenerators, thus forming a thermal feed from the low-pressure cycle tothe high-pressure cycle.
 32. The power generation system according toclaim 31, wherein the first set of one or more compressors deliverscompressed air to the cold-flow passages of the first set of one or moreheat regenerators so that heated compressed air is fed to the cathodeflow passages of the one or more fuel cells, while a compressed andheated gaseous fuel is fed to the anode flow passages of the one or morefuel cells, the one or more fuel cells generate electricity byelectrolytic oxidation reaction that takes place in the fuel cellelectrolyte layer at a high-temperature, between a portion of the fuelfed to the anode flow passages and a portion of the oxygen in thecompressed air stream fed to the cathode flow passages; and wherein thehot gas streams expelled by the anode and cathode flow passages are fedto a post-combustor where the unreacted fuel is allowed to complete itsoxidation reaction by combining with the oxygen in the hot compressedair stream, the post combustor thus expels a hot flue gas streamcomprising the combustion products.
 33. The power generation systemaccording to claim 32, wherein the low-pressure flue gas stream expelledby the post-combustor passes through the third set of heat regenerators,thus rejecting heat to the high-pressure cycle; wherein the low-pressureflue gas stream expelled by the third set of heat regenerators is fed tothe first set of the one or more expanders, the first set of the one ormore expanders producing mechanical power in turn to drive the one ormore alternating current (AC) electricity generators, the flue gasexpands in the first set of one or more expanders to near-atmosphericpressure; wherein the expanded flue gases expelled by the first set ofone or more expanders pass through the hot passages of the first set ofheat regenerators in a series arrangement from the highest temperatureregenerator to the lowest temperature regenerator; and wherein the fluegas stream having rejected heat, now at near-atmospheric pressureescapes to the atmosphere.
 34. The power generation system according toclaim 33, wherein the gas stream that expands in the second set of oneor more expanders in the high-pressure cycle expands until the pressurereaches near-operating pressure of the fuel cells, the gas expelled bythe second set of one or more expanders and the flue gas expelled by thethird set of heat regenerators of the low-pressure cycle are combined toform a single combined flue gas stream, the single combined flue gasstream is fed to the first set of one or more expanders in thelow-pressure cycle; and wherein the flue gas stream, having expanded inthe first set of one or more expanders, passes through the hot passagesof the first set and the second set of heat regenerators such that theflue gas stream flows from the highest temperature heat regenerator tothe lowest temperature heat regenerator in the sequence of progressivelydecreasing temperature.
 35. The power generation system according toclaim 33, wherein the power generation system comprises a thermal feedto a bottoming cycle placed after the second set of one or moreexpanders, but prior to the second set of one or more heat regeneratorsin the high-pressure cycle; wherein the bottoming cycle is a closed-loopcycle as described in claim 5.